White paper: Deploying Citrix XenServer 5.0 with Dell equal Logic PS Series storage

The Dell EqualLogic PS5000E line spans from 2 to 16 TB in capacity in a single array, utilizing SATA drives

ranging from 250GB to 1TB. The PS5000X arrays offer 6.4TB or raw storage capacity utilizing 400GB,

10,000 RPM Serial Attached SCSI (SAS) disk drives. The PS5000XV arrays use 146GB or 300GB 15,000

RPM Serial Attached SCSI (SAS) disk drives to deliver 2.3TB or 4.8TB of raw capacity, respectively. The

PS5500E array utilizes 48 7200 RPM 500GB or 1TB SATAII drives to deliver 24 or 48 TB of raw capacity

in a 4U enclosure.

Performance and capacity may easily be scaled by adding additional PS Series arrays. All PS Series

models have dual controllers with three 1GbE ports per controller, for a total of six 1GbE ports.


XenServer 5.0 Dell Edition


With the 64-bit open-source Xen hypervisor at its core, Citrix® XenServerDell Edition is a powerful

virtualization solution that enables efficient resource consolidation, utilization, dynamic provisioning, high

availability and integrated systems management. XenServer Dell Edition has a small foot print and is

optimized to run from an internal flash storage in Dell PowerEdgeservers. Dell and Citrix have partnered

to bring pre-qualified and virtualization-ready platforms for today’s dynamic and growing data centers.

What’s new in XenServer 5.0 Dell Edition?

Expanded hardware and systems management support

Expanded Server Support—XenServer 5.0 is now supported on an expanded list of Dell PowerEdge

servers. PowerEdge 1950 III, 2900III, 2950III, R805, R900, R905, M805 and M905 are now fully qualified

and supported to run XenServer 5.0.

Expanded Storage Support—Storage arrays supported by Dell with XenServer 5.0 include

Dell PowerVaultMD1000, MD1120, MD3000, MD3000i and Dell EqualLogic PS5000 arrays.

XenServer 5.0 also includes a new Dell EqualLogic PS Series Storage Adapter that not only simplifies

virtual machine storage management, but also enables advanced PS Series features to be used by

XenServer hosts.

OpenManage 5.5—With Dell OpenManage5.5 integrated in XenServer 5.0, customers can easily

monitor and manage server hardware and direct attached storage from a simple to use web user

interface or CLI. Dell Remote Access Controller (DRAC) 5 provides out of band, including full KVM

and virtual media, access to the server.

Faster and more powerful

Powered by Xen—Boasting faster out-of-the-box performance, Citrix XenServer 5.0 gets more virtual

machines, with more users and faster applications onto Dell’s 64-bit PowerEdge servers. The Xen® 3.2

hypervisor includes control domain performance tuning, updated paravirtualization drivers and VHD

performance tuning.

Tuned for Windows—XenServer adds support for Windows Server 2008, has been optimized to run

Windows-based workloads and has been certified on both 32-bit and 64-bit versions of Windows

Server through Microsoft’s Server Virtualization Validation Program (SVVP).

Tuned for XenApp—Citrix XenAppusers benefit from XenServer’s memory management

performance enhancements for XenApp workloads. More users and faster applications lead to more

efficient application delivery with XenApp.


Simplified management

Usability enhancements—XenServer 5.0 includes 30 new ease-of-use enhancements to make it

simpler for customers to use the XenServer platform.

Search, sort and tag—The XenCentermanagement console allows administrators to tag and

search virtual infrastructure with ease to keep track of virtual machines as they proliferate across

large datacenters. Web 2.0 style tagging and searching capabilities allow IT professionals to assign

metadata and virtual tags to workloads, either pre-defined or customized to each organization’s needs.

Performance monitoring and alerts—XenCenter includes performance monitoring, trending and

alerting. Easily track key performance statistics for virtual and physical servers to identify hot spots,

balance computing resources and alert administrators about potentially detrimental server behavior

or changes.

Wizard driven—XenServer includes new Wizard-driven utilities such as XenConvert which transforms

physical servers into virtual machines in minutes. The XenCenter management console also includes

new wizards for advanced storage and server networking configurations.

Disaster proof

Automated high availability—XenServer adds automated high availability (HA) with resource-based

placement of virtual machines in the event of server failures. Automated HA includes dynamic

fail-over planning based on available resources to help ensure that virtual machines always restart

on the appropriate physical server.

XenCenter self-healing—XenCenter combines new automated HA with its distributed management

architecture to create a self-healing, hard to kill management console. Every server in a resource pool

can be a fail-over target for the XenCenter management console.

Disaster recovery—XenServer includes enhanced support for SAN based remote replication and

auto-backup of virtual machine configuration to remote sites.

The only dynamic provisioning game in town

Windows Server 2008 and Hyper-V support—XenServer now includes the ability to stream

Windows Server 2008 workloads to physical servers or even Hyper-V (and associated workloads)

to bare metal servers for dynamic provisioning of server workloads.

Additional Microsoft integration—Role based administration using Active Directory, virtual hard disk

(VHD) compatibility and out-of-the-box integration with Microsoft SQL Server are just a few of the many

Microsoft related enhancements in XenServer’s dynamic provisioning capabilities.


EqualLogic PS Series and


Dell EqualLogic PS Series iSCSI arrays simplify storage deployment by offering high performance,

reliability, intelligent automation, and seamless virtualization of a single pool of storage. A PS Series

SAN provides intelligent automation of storage management as well as virtualized storage assets. With

single console management and ease of storage provisioning, an EqualLogic PS Series SAN increases

the power and flexibility of a virtual infrastructure. The arrays present a single virtualized pool of storage

resources to attached servers. Additional arrays can be seamlessly added into an existing SAN to

automatically increase storage pool resources without disruption of application or data availability.

Dell EqualLogic storage brings unique benefits to the Citrix XenServer virtualization solution.

Optimized utilization

While XenServer provides an excellent virtualization platform to consolidate and optimize server

resource usage, EqualLogic PS Series storage arrays optimize storage utilization by dynamically

balancing loads among multiple storage arrays as the usage changes. Additionally one can configure

thin-provisioned volumes to grow on-demand only when additional storage is needed for those

volumes. Thin-provisioning can increase the efficiency with which the storage resources are utilized.

The XenServer EqualLogic Storage Adapter allows thin volumes to be created from the XenCenter

interface or using XenServer CLI, thus optimizing storage requirement and simplifying storage

deployment for virtual machines.

Reduced deployment time and effort

EqualLogic PS Series arrays reduce the time and effort required to deploy a SAN. Inside the

EqualLogic PS Series Group Manager, one can easily create new volumes and assign them to

XenServer hosts, which can immediately access those volumes as storage repositories. Using the

XenServer EqualLogic Storage Adapter, a volume on the PS Series Group is automatically created as

a virtual hard disk for a virtual machine and access controls are automatically set for the volume. Using

the volume cloning feature of PS series, new virtual machines can be instantly provisioned by cloning

an existing virtual machine.

Reduced management complexity

EqualLogic PS Series SANs simplify storage management by consolidating physical storage and

providing a single-pane management view of the entire virtualized storage pool in the Group. The PS

Series intelligently balances workloads across the available arrays without need for human intervention,

automatically adapting to changes in workload.

The XenServer EqualLogic Storage Adapter integrates the PS series storage management directly into

the XenServer and XenCenter interface. Storage volumes for virtual machines can be managed right

from XenCenter or XenServer CLI. Thus virtual machine storage deployment and management are

greatly simplified when using EqualLogic storage with XenServer.


High availability

XenServer 5.0 introduces an automated local High-Availability feature that protects virtual machines

hosted on shared storage against host failures. The virtual machines running on a failed host are

restarted on remaining servers in the XenServer pool. NIC bonding available in XenServer protects

against failures in either network cards or paths for storage, virtual machine or management traffic.

EqualLogic PS Series arrays offer best in class reliability, with hot-swappable and fully redundant

components, RAID 5/10/50 support and hot spares.

High scalability

As one adds more PS Series array members to a PS Series group, the storage capacity scales along

with the performance without disrupting application or data availability. Plus the SAN dynamically

balances the load to optimize storage resources.

Using XenServer Resource Pools, once can easily add new XenServer hosts to an existing pool,

increasing the pool’s capacity to meet increased workload demands.

Increased flexibility

The net result of all these features and capabilities is not only a reduced TCO, but increased flexibility.

The ease and speed with which you can add new virtual servers or expand physical storage,

combined with single-pane management and the security of a high-availability infrastructure, allows IT

administrators to respond quickly and flexibly to enterprise demands and initiatives.

SAN features like tiering, load balancing, advanced features in replication and snapshots provide a

higher level of functionality that you can’t find in standard stand-alone direct attached storage.


XenServer storage model and


XenServer host defines a container called a Storage Repository (SR) to describe a particular storage

target, in which Virtual Disk Images (VDIs) are stored. A VDI is a disk abstraction which contains the

contents of a virtual disk. Figure 1 illustrates the overall storage model in XenServer.

The interface to storage hardware allows VDIs to be supported on a large number of SR types. With

built-in support for IDE, SATA, SCSI and SAS drives connected locally, and iSCSI, NFS and Fibre

Channel connected remotely, the XenServer host SR is very flexible. The SR and VDI abstractions

allows advanced storage features such as sparse provisioning, VDI snapshots, and fast cloning to

be exposed on storage targets, such as Dell EqualLogic PS Series, that support them. For storage

subsystems that do not inherently support advanced operations directly, a software stack is provided

based on Microsoft’s Virtual Hard Disk (VHD) specification which implements these features.

Each XenServer host can use multiple SRs and different SR types simultaneously. These SRs can be

shared, or dedicated between hosts. For shared SR, shared storage is pooled between multiple hosts

within a defined resource pool. A shared SR must be accessible to each host, and thus must be on

iSCSI, NFS, Fibre Channel or Direct Attached for clusters (such as Dell PowerVault MD3000) storage.

Finally, all hosts in a single resource pool must have at least one shared SR in common.

The following four object classes that are used to describe, configure, and manage storage:

Storage Repositories (SRs) are storage targets containing homogeneous virtual disks (VDIs). SR

commands provide operations for creating, destroying, resizing, cloning, connecting and discovering the

individual Virtual Disk Images (VDIs) that they contain. A storage repository is a persistent, on-disk data

structure. So the act of “creating” a new SR is similar to that of formatting a disk—for most SR types,

creating a new SR involves erasing any existing data on the specified storage target. The exception is

NFS SRs, which create a new directory on the filer leaving existing NFS SRs as they were. SRs are longlived,

and may in some cases be shared among XenServer hosts, or moved between them.

Physical Block Devices (PBDs) represent the interface between a physical server and an attached

SR. PBDs are connector objects that allow a given SR to be mapped to a XenServer host. PBDs store

the device configuration fields that are used to connect to and interact with a given storage target. For

example, NFS device configuration includes the IP address of the NFS server and the associated path

that the XenServer host mounts. PBD objects manage the run-time attachment of a given SR to a

given XenServer host.


Virtual Disk Images (VDIs) are on-disk representation of virtual disks provided to VMs. VDIs are the

fundamental unit of virtualized storage in XenServer. Similar to SRs, VDIs are persistent, on-disk objects

that exist independently of XenServer hosts.

Virtual Block Devices (VBDs) are connector objects (similar to the PBD described above) that allow

mappings between VDIs and Virtual Machines (VMs). In addition to providing a mechanism to attach

(or plug) a VDI into a VM, VBDs allow the fine-tuning of parameters regarding QoS (quality of service),

statistics, and the bootability of a given VDI.

Figure 1: XenServer Storage Model








Dell EqualLogic PS Series

feature definitions

This section describes some important PS series definitions relevant to this paper. Refer to PS Series

online help for detailed information on various definitions and features.


A volume is a logical device representing a portion of storage pool space and seen on the network

as an iSCSI target. Volume data is divided among pool members. Volumes are protected by access

control records.

Thin provisioning

Thin provisioning technology allows one to more efficiently provision storage, while still meeting

application and user storage needs. A volume has two capacity sizes associated with it:

The reported size is the size that is seen by iSCSI initiators. Hosts connected to the volume will

associate this amount of space with the volume.

The volume reserve is the amount of space that is allocated to the volume.

For a volume without thin provisioning enabled, the reported size and the volume reserve are the same.

For volume with thin-provisioning enabled, the reported size is greater than (or equal to) the volume

reserve, because the volume is not fully allocated.

A thin-provisioned volume is initially allocated only a portion of the volume size. As data is written to

the volume, more space is automatically allocated (if available), and the volume reserve increases up to

a specified limit. Regular event messages occur as space is used, giving you the opportunity to make


Because thin-provisioned volumes are only allocated the storage space that they actually use, you can

more efficiently use storage resources, with no difficult resize operations on the computer.

Thin provisioning is most effective when you know how a volume usage will increase over time, the rate

of growth is predictable, and users do not need immediate, guaranteed access to the full volume size.

Administrators must monitor thin-provisioned volumes and be prepared to increase storage space by

adding or moving arrays to the pool containing the volume. If you must guarantee the full volume size,

thin provisioning is not recommended.

Volume snapshots

A snapshot is a space-efficient point-in-time representation of volume data. Snapshot creation does

not disrupt access to the volume.

Like volumes, snapshots on the network look like iSCSI targets and can be set online and accessed by

computers with iSCSI initiators. You can recover volume data by restoring a volume from a snapshot or

by cloning a snapshot, which creates a new volume.


To create a snapshot, one must first reserve snapshot space for the volume. Snapshot reserve is taken

from the pool containing the volume, and is based on a percentage of the current volume reserve.

Group level defaults can be set to reserve a specified percentage of volume size for snapshot reserve.

PS Series group snapshot technology uses a reallocate-on-write technique. When users make changes

to the base volume (or to the snapshot), the group stores the changes in the snapshot reserve.

Volume clones

A volume clone is an exact copy of a volume created from either the original volume or from a snapshot

or replica. Cloning a volume creates a new volume with a new name and iSCSI target, but the same

size, contents, and thin provisioning settings as the original volume at the time of the cloning. The

new volume is created in the same pool as the original volume and is available immediately. Cloning a

volume does not change the original volume.

A cloned volume consumes 100% of the original volume size from free space in the pool. If you create

snapshots or replicas of the new volume, they will use additional pool space. You cannot select a

different storage pool (if available) during the clone operation, but you can move the new volume to

another pool later.

Volume replicas

Replication technology in the PS Series firmware lets you copy volume data between groups, thereby

protecting the data from a variety of failures, ranging from the destruction of a volume to a complete

site disaster, with no effect on data availability or performance. Similar to a snapshot, a replica is a copy

of a volume at a specific point in time. A replica set is the set of replicas for a volume created over time.

A volume and its replica set are always stored in different groups. By separating the groups

geographically, volume data is protected against a complete site disaster. To replicate data between

two PS Series groups, you must configure the groups as replication partners. The groups can be in the

same building or an unlimited distance apart.

Each replication partner plays a specific role in the replication of a volume. The volume is stored on

the primary group, while the volume replica set is stored on the secondary group in space that the

secondary group delegates to the primary group. The primary group sends (replicates) the data and

the secondary group receives the data. Mutual authentication offers security between partners.

The first replication of a volume sends the entire contents of the volume to the secondary group.

In subsequent replications, only the data that changed since the previous replication is sent to

the secondary group. The longer a replication takes, or the longer the interval between scheduled

replications, the more the data that might have to be transferred to the partner.

To recover volume data from replicas in the secondary group, you can clone an individual replica to

create a new volume. You can also host a volume on the secondary group, either temporarily, for

example to do backups, or permanently (e.g. to replace a failed primary group or to change the roles of

the primary and secondary groups).

If you are hosting the volume temporarily on the secondary group, you can later fail back to the primary

group and use the original replication configuration.


iSCSI storage repositories in

XenServer 5.0

XenServer 5.0 hosts can access iSCSI storage using the built in open-iscsi software initiator or an

iSCSI HBA. XenServer 5.0 includes support for two types of iSCSI storage repositories:

LVM over iSCSI or lvmoiscsi SR: utilizes the Linux Volume Manager (LVM) to create a logical volume

per virtual disk image (VDI) on the iSCSI LUN. The VDIs residing in LVM over iSCSI SRs do not provide

support for sparse provisioning or fast cloning. The SR utilizes the entire LUN specified at creation time

and may not span more than one LUN.

Dell EqualLogic or equal SR: utilizes the XenServer EqualLogic Storage Adapter to manage virtual

machine storage on PS Series Group. For each SR of type Dell EqualLogic, a small management

volume is created on PS Series Group. For each XenServer virtual disk image (VDI) in the SR, a

corresponding volume on PS series group is created. This allows for advanced VM life cycle operations

such as snapshots, fast clones, thin provisioning, volume resizing etc.

Both LVM over iSCSI and Dell EqualLogic SRs are capable of supporting VM agility using XenMotion:

VMs can be moved across XenServer hosts in a pool without noticeable downtime. CHAP support is

provided for client authentication, during both the data path initialization and the LUN discovery phases.


LVM over iSCSI vs. Dell EqualLogic

SR usage considerations

When using EqualLogic PS Series to provide iSCSI storage, you should consider storage and feature

requirements to decide whether to use the specialized Dell EqualLogic SR, or to use the generic

LVM over iSCSI SR. The specialized XenServer EqualLogic Storage Adapter enables XenServer to

communicate with the PS Series group to manage storage for VMs and use advanced array features

such as thin provisioning, fast cloning and snapshots. Table 1 below summarizes comparison between

the LVM over iSCSI and EqualLogic SR capabilities.

Features/ Requirements LVM over iSCSI SR Dell EqualLogic SR

Shared SR for XenServer Pool Yes Yes

XenMotion Yes Yes

Resize Virtual Disk Image (VDI) Yes Yes

Thin Provisioning No Yes

Fast Cloning No Yes

Virtual Machine Snapshots No Yes

PS Series volume management from


No Yes

Number of volumes on PS Series per


One for SR; each VDI is a logical


One for SR plus one for each VDI

iSCSI connections per host to PS

series group

One per SR One per active VDI

Connection load balancing for an SR

on PS series group

From a host, connection to an SR

through a single iSCSI port on a


Connections to VDI volumes load

balanced across member iSCSI ports

Table 1: LVM over iSCSI Vs EqualLogic SR


Setup and configuration

A simple setup utility lets you quickly configure a PS Series array as a member of a new group.

After you choose the RAID type, the array is automatically configured, and the storage is immediately

ready for use. Data and network I/O are automatically load balanced across the disks and network

interfaces—with no impact on data availability.

To increase SAN capacity and performance, connect another array to the network and add it to the

group. Load balancing across the members occurs automatically, as needed. Management overhead

remains the same, regardless of the group size.

For instructions on initial PS series array configuration, please refer to the PS Series Quick Start Guide


Typical PS Series-XenServer setup

This section describes a typical multi XenServer host setup with EqualLogic PS Series Group. As shown

in Figure 2, Citrix XenServer Dell Edition runs on Dell PowerEdge servers, configured in a resource pool.

All XenServer hosts are connected via an Ethernet fabric and share storage on the Dell EqualLogic

PS5000 array(s). The iSCSI traffic is physically isolated from other network traffic using separate physical

Ethernet switches. Two NICs on each host are bonded to provide high availability and load balancing for

host management and virtual machine traffic and high availability for IP storage traffic.

Figure 2: A sample of typical XenServer Pool Configuration using PS Series storage

This configuration illustrates traffic segregation using separate physical switches; however, isolation can

also be achieved using VLANs. XenCenter can be installed on any workstation or server machine that

has access to the host management network.

Note: Refer to XenServer Dell Edition Solution Guide for more information on supported Dell storage configurations with XenServer.

EqualLogic PS

Series Array

XenCenter Client /

Management Station



XenServer Management and

XenMotion Traffic

Virtual Machine Traffic

iSCSI Storage Traffic



2 2








Multi-pathing with XenServer and PS Series

Multi-pathing in XenServer for iSCSI traffic is achieved using a highly available bond device on the

XenServer host. In case of failure of a network port, the other network port in the bond takes over the

network traffic. As shown in Figure 2, it is recommended to use redundant Ethernet switches to prevent

a path failure at the switch level. Note that load balancing for network traffic over a bond is supported

only for virtual machine traffic and not for IP storage traffic. At any given time, only one NIC, out of two in

a bond, is used for iSCSI traffic. If the active NIC in a bond fails, the other NIC will take over. Refer to the

XenServer 5.0 Reference Manual for more information on creating and managing NIC bonds.

The EqualLogic PS arrays have two controllers; only one controller is active at a given time. Each

controller has 3 network ports for iSCSI connectivity. The XenServer hosts connect to the PS Series

Group using the well known address or the Group IP address rather than the IP address of an iSCSI

port on a member array. When an initiator connects to the PS Series Group using the Group IP

address, the group redirects the initiator (via iSCSI redirect functionality) to log-in to an iSCSI port on

a member. The PS series group intelligently redirects incoming connections to load-balance iSCSI

traffic across iSCSI ports on group members. In case a port on a controller fails, the connections are

redirected to other available ports. In case the active controller fails, the passive controller on a member

becomes active and takes over IP settings of the failed controller.

Note: XenServer 5.0 natively uses dm-multipath for iSCSI traffic where the iSCSI storage arrays expose multiple target portals.

However this is not the case with EqualLogic PS arrays. For this reason, enabling multi-pathing for a XenServer host using

XenCenter or CLI does not use dm-multipath functionality.

Sample XenServer host and PS Series network configuration

This section discusses a sample network configuration for a XenServer host and a PS Series group

to create a configuration as illustrated in Figure 2. Figure 3 shows the XenServer host network

configuration. The host has four Gigabit LOM ports and two single port Gigabit network adapters.

Using 2 NIC ports each, three bond devices (for host management, IP storage and virtual machines)

are created using the XenCenter interface. In XenServer, the host management interface is used for the

IP traffic by default. However, as a best practice it is recommended to use a separate host interface

for IP storage traffic. This is achieved by creating another host interface on a subnet separate from the

host management interface.

1. Using XenCenter interface, create a bond device for host management and virtual machine

network. Active/active bonding in XenServer 5.0 provides both high availability and load balancing

for virtual machine and host management traffic. Figure 4 shows the host management interface as

seen in XenCenter interface.

2. To provide high availability for storage traffic, create a bond using two NIC ports.

3. Create a new host interface for storage traffic: in XenCenter interface, click on the host and select

“Management Interfaces.Create a new interface and configure the IP settings such that the

storage management interface is on a separate subnet from the host management interface, and

on the same subnet as the PS Series Group. Figure 4 shows storage interface as seen in the

XenCenter interface. Note that the storage interface must be on a separate subnet from the host

management interface to segregate IP storage traffic from host management traffic.

Example XenServer Host IP configuration:

Host Management Interface:

Host Storage Interface (bond):


Figure 3: Sample host management and storage networks on a XenServer host

Figure 4: XenServer Host Networking: Management and Storage Interfaces

Note: As a best practice, it is recommended to use a static IP address for host management and storage interface.

Example IP configuration for a PS Series group with one member:

PS Series Group and member IP configuration:

PS Series Group IP:

PS Series Member Storage Port (eth0):

PS Series Member Storage Port (eth1):

PS Series Member Storage Port (eth2):

Note: PS Series network configuration requires that the Group IP and the IPs for the member storage ports (eth0, eth1 and eth2)

must all be on the same subnet.

If using a separate management IP (other than the Group IP) to manage a PS Series group, then the

Group IP and storage ports eth0 and eth1 need to be on same subnet. The management IP and eth2

for the members should be on the same subnet. For more information on configuring a management

interface (other than the group interface) for a PS Series group, refer to the PS series online help.

Networking best practices for PS Series and XenServer

Refer to the PS Series Array Network Performance Guidelines document for information on general

network configuration best practices for EqualLogic PS Series arrays.

Note: Jumbo frames are not supported in XenServer 5.0.

Note: XenServer 5.0 natively uses dm-multipath for iSCSI traffic where the iSCSI storage arrays expose multiple target portals.

However this is not the case with EqualLogic PS arrays. For this reason, enabling multi-pathing for a XenServer host using

XenCenter or CLI does not use dm-multipath functionality.


Creating a storage repository on

PS Series Group

Creating a storage repository of type LVM over iSCSI (lvmoiscsi)

1. Following the instructions available in the PS Series online help, configure the PS Series array,

create a group, set a member RAID policy, create a volume and set appropriate access control

method (using XenServer host IQN or management IP).

2. If creating an SR for a pool, make sure that the storage volume is enabled for shared access from

multiple initiators. To enable shared access, in the PS series group manager user interface, rightclick

on the volume and select “Modify Volume Settings.” Select the Advanced tab and check

“Enable shared access to the iSCSI target from multiple initiators” (See Figure 5).

Figure 5: Enable shared access to the SR volume when SR is intended to be shared

3. Using the XenCenter interface, right-click on the XenServer host or the pool for which you would

like to create SR for and select “New Storage Repository.” Choose the iSCSI radio button for the

type of new storage, and select “Next.

4. Enter the name for the new SR in the name field, PS series Group IP address in the Target Host

field, and 3260 in the port field. Provide the chap username and password information if configured

for the volume. Then click on “Discover IQNs” to perform target discovery. Each volume on a PS

Series array has a unique target name with LUN ID set to “0.” Select the appropriate IQN and then

click on “Discover LUNs” to discover the LUN or volume associated with the target. Select the

volume and click “Finish” to create a new SR.


Creating a storage repository of type Dell EqualLogic (equal)

Note: To use an SR of type Dell EqualLogic, the firmware version of PS Series arrays must be 4.0.1 or higher.

To create a storage repository of type Dell EqualLogic or equal, follow the steps below:

1. Following the instructions available in the PS Series online help, configure the EqualLogic array,

create a group, set a member RAID policy, and create a volume.

2. Using the PS Series Group Manager User Interface, make sure that SSH access is enabled on

the group members. Click on the “Group Configuration” and select the “Administration” tab. If not

already enabled, check the “Enable SSH (secure shell)” access checkbox in the CLI access options

for the group and save the configuration.

3. Using the XenCenter interface, right-click on the XenServer host or the pool for which you

would like to create SR for and select “New Storage Repository.

4. In the “Choose the type of new storage window”, select “Dell EqualLogic” (see Figure 6) and

click “Next.

Figure 6: Select Dell EqualLogic to create an SR of type Dell EqualLogic

5. In the “Enter the Dell EqualLogic filer details” window, provide a name for the SR in the name

field, the Group IP of your PS Series group, and the user name and password for an account with

administrative privileges for group or a pool. Optionally, provide CHAP credentials if set on the PS

Series group and click “Next.

6. The following screen provides two options: Reattach an existing SR or create a new SR. Choose

the “Create a new SR on the following storage pool” radio button. You can see the details on the

available storage pool including the size, free available space, number of existing volumes and

members in the pool.

If you like all VDIs in the SR to be thin provisioned, select the “Thin Provisioning” checkbox when

creating the new SR (see Figure 7).

Click “Finish” to create a new SR.


Figure 7: Select the appropriate storage pool and thin provisioning settings for EqualLogic SR

As shown in Figure 8, upon completion of the SR creation process, a corresponding volume of size

20MB is created on the PS Series Group. When adding an SR to the pool, access control records for

all XenServer hosts in the pool are added to the volume. The access control is specified by the IQN of

the XenServer host.

Note: Volume name and description fields are used by XenServer EqualLogic Storage Adapter to manage volumes on the PS Series

Group. Do not manually change the name and description fields for any volume automatically created by a XenServer host.

Figure 8: SR volume as shown in PS Series Group GUI


Identifying XenServer storage objects on a PS Series Group

For Dell EqualLogic SR, an SR is just a logical grouping of VDIs or volumes on the PS Series Group.

The naming scheme for volumes automatically created by XenServer EqualLogic Storage Adapter is

as follows:

At the point the SR is created, a management volume is provisioned on the PS Series Group. This

serves to identify the persistent SR presence on the group, as well as providing a location to store SR

metadata as required by XAPI. The management volume is named as:


where SR_UUID is the UUID of the storage repository.

For example, in Figure 9, the volume


corresponds to an SR with UUID b93f1728dd0c6077e96dbc968a047fb2

Each volume corresponding to a VDI within an SR is identified by the identification string “XenStorage”

followed by the SR UUID, and a cropped version of the VDI UUID. The full VDI UUID is stored in the

Volume description field.

For example, as shown in Figure 9 the volume with name


corresponds to a VDI. The VDI is related to SR with UUID b93f1728dd0c6077e96dbc968a047fb2

and the cropped UUID of VDI is 2332cdcae4fd4a3d9bbc. The full UUID of VDI is available in the

volume description.

Figure 9: A VDI volume as shown in PS Series Group GUI

Note: The XenServer EqualLogic Storage Adapter uses volume name and description fields to reference volumes on PS Series

Group. Manually changing either the volume name or description fields to values other than those assigned by the XenServer

storage adapter may lead to failure in storage management tasks.


Typical lifecycle tasks for VMs on

Dell EqualLogic SR

This section describes typical virtual machine life cycle operations for virtual machines created and

managed using the XenServer EqualLogic Storage Adapter.

Create a virtual machine

The process to create a virtual machine with storage on Dell EqualLogic PS series group remains the

same as with any other storage backend. While creating a VM, just select the appropriate SR created

on your PS Series Group. For more information on creating virtual machines, refer to XenServer Virtual

Machine Installation Guide.

Create a VDI

When using an SR of type Dell EqualLogic, for each Virtual Disk Image (VDI) created on a XenServer

host, a corresponding volume is created on the PS Series Group. Figure 9 shows a volume, with name

XenStorageb93f1728dd0c6077e96dbc968a047fb22332cdcae4fd4a3d9bbc, that has been

automatically created by the XenServer EqualLogic Storage Adapter.

The size of the volume on the array is same as the VDI size specified by the user.

Note: When a VDI is created using XenCenter, the corresponding volume created on the PS series Group inherits the default group

volume and thin provisioning settings.

To create a VDI using CLI use the xe vdi-create command:

# xe vdi-create virtual-size=10GiB name-label=testvdi

sr-uuid=<SR UUID> type=user sm-config:allocation=<thin | thick>

sm-config:snap-reserve-percentage= <Percentage Integral Value>

sm-config:snap-depletion=<delete-oldest | volume-offline>

where SR_UUID is the UUID of the SR of type Dell EqualLogic

sm-config:allocation controls whether the VDI volume is provisioned as a thin volume or not. Setting

sm-config:allocation=thin will create a volume with thin provisioning enabled. Setting

sm-config:allocation=thick will create a volume with thin provisioning disabled. If type of

allocation is not specified, the default allocation for the SR is used to provision the VDI volume.

sm-config:snap-reserve-percentage specifies amount of space, in terms of percentage of

volume, to reserve for volume snapshots. If snap-reserve-percentage is not specified, the group

default value for snapshot reserve is used.

sm-config:snap-depletion specifies the snapshot space recovery policy:

action taken when the space reserved for snapshots has been exceeded. Setting

sm-config:snap-depletion =delete-oldest deletes the oldest snapshots until sufficient

space is recovered (the default). Setting sm-config:snap-depletion=volume-offline sets

the volume and snapshots offline. Active iSCSI connections will be terminated before a snapshot is

automatically deleted.


For example, the following command to create a new VDI

# xe vdi-create virtual-size=10GiB name-label=vdi1 type=user

sr-uuid=b93f1728-dd0c-6077-e96d-bc968a047fb2 sm-config:allocation=thin

sm-config:snap-reserve-percentage=50 sm-config:snap-depletion=delete-oldest

provisions a volume, on PS Series Group, of size 10GB, with a snapshot reserve of 50% of volume size

(10GB), thin provisioning enabled and snapshot space recovery policy to delete oldest snapshot.

Delete a VDI

Deleting a VDI deletes the associated volume on the PS Series Group. However if a VDI has any

associated snapshot, deleting a VDI from XenServer host will not delete the parent volume on PS

series Group until the last existing snapshot is deleted.

A VDI can be deleted or destroyed using the XenCenter interface or using a vdi-destroy command.

# xe vdi-destroy uuid=<VDI_UUID>

Resize a VDI

To resize a VDI from XenCenter, right click on the VDI and select Edit Virtual Disk. Modify the size of the

VDI and click OK.

To resize a VDI using CLI, use the xe vdi-resize command:

# xe vdi-resize uuid=<VDI_UUID> disk-size=<new size>

where VDI_UUID is the UUID of the VDI under consideration

new size the new size of the VDI.

For example, the following command sets the size of the VDI to 50GB:

# xe vdi-resize uuid=6be5ed34-7600-4218-a68e-741aeb4ee815 disk-size=50GiB

When a VDI is resized using XenCenter or CLI, the size of the corresponding volume on PS series

group is also set to the new size value specified for the VDI. The snapshot reserve for the volume is

also automatically adjusted to comply with the predefined percentage of volume size.


Copy or clone a VM

A copy or clone of a VM can be created in two ways:

Fast Clone—Uses PS Series volume clone feature to instantaneously create clones of volumes

corresponding to VDIs attached to the virtual machine.

Full Copy—Creates a copy of the source virtual machine storage volumes by copying all data over to

new volumes. Depending on the size of data to be copied, a full copy operation may take from a few to

several minutes to complete.

The XenServer fast cloning feature utilizes PS Series volume cloning to provision new virtual machines

within seconds. To provision a new VM using fast cloning, right click on the source VM and select

“Copy VM.” Provide a name and description for new VM and select “Fast Clone” as the copy mode

(see Figure 10). Click “Copy” to finish creating a new VM that is a copy of a specified source VM.

Figure 10: Fast cloning feature uses PS Series volume cloning to instantaneously provision new VMs

Deploy from Template

A template is a “gold image” that contains all the configuration settings to instantiate a specific VM.

With XenServer one can create VMs, configure them in standard forms for particular needs, and save a

copy of each as a template for future use in VM deployment.

If all the VDIs of the template VM reside on an SR of type Dell EqualLogic, when deploying a new VM,

in the same SR, from the template, XenServer uses the PS Series cloning feature to instantaneously

provision a new virtual machine. However if a VM is deployed to an SR other than the SR where

template resides, XenServer provisions the new VM by copying.


Snapshot a VM

XenServer provides a convenient VM snapshot mechanism that can take a snapshot or capture a

point-in-time copy of a VM’s storage and metadata. Where necessary, I/O is temporarily halted while

the snapshot is being taken to ensure that a self-consistent disk image can be captured.

Snapshot operations result in a snapshot VM that is similar to a template. The VM snapshot

contains all the storage information and VM configuration, including attached VIFs, allowing them

to be exported and restored for backup purposes. XenServer 5.0 also includes a Xen VSS provider

(installed as part of Citrix XenTools) to enable quiesced snapshots. Quiesced snapshots take

advantage of the Windows Volume Snapshot Service (VSS) for services that support it, so that a

supported application (for example Microsoft Exchange or SQL Server) can flush data to disk and

prepare for the snapshot before it is taken.

For virtual machines residing on SR of type Dell EqualLogic, when a snapshot operation is issued,

XenServer EqualLogic Storage Adapter instructs the PS Series Group to take a snapshot of the

volumes associated with the virtual machine’s VDIs. Snapshots are supported for only Dell EqualLogic

SRs and not for an SR of type LVM over iSCSI.

A snapshot on the PS series is treated as a separate target and gets its own IQN. When virtual

machine snapshots are created from a XenServer host, access control records (specified by host IQN)

for the snapshots are automatically created to allow the XenServer or a group of XenServer hosts in a

pool to access the snapshots.

Figure 11 shows a virtual machine win2003_vm1 which has two VDIs. Under the Virtual Disks tab on

XenCenter, snapshots for the VDIs appear for each VDI. The corresponding view on PS Series GUI is

shown in Figure 12.

Figure 11: VM snapshots as shown in XenCenter Interface

Figure 12: VM snapshots as shown in PS Series Group UI


XenServer treats snapshots as templates. As seen in Figure 11, the snapshot win2k3_vm1_snap1 of

virtual machine win2k3_vm1 is also listed as a custom template. Just like regular templates, one can

instantaneously deploy new virtual machines from such snapshots. When a new VM is deployed from a

snapshot, XenServer uses the snapshot clone feature of the PS series arrays to instantaneously create

clones of snapshots associated with the source VM. Access control records (specified by host IQN) for

newly cloned volumes are automatically created to allow a XenServer or a group of XenServer hosts in

a pool to access the volumes.

Refer to the XenServer Reference Guide for more information on regular and quiesced snapshots.

Restore a VM from a Snapshot

A virtual machine can be restored to a snapshot state if needed. One can restore the VDI volumes

on PS series from snapshots; however one must restore all volumes attached to a VM. Another

way to restore a VM from the snapshot state is to create a new virtual machine from a snapshot

and deactivate or delete the old VM. Follow the steps in the VM Rollback section in XenServer 5.0

Reference Guide for instructions on how to restore a VM from a snapshot.

Delete a VM

When a VM is uninstalled, all the volumes, on the PS Series Group, associated with the virtual machine

are deleted. When the volumes are deleted, the storage space is marked as free and returned to the

storage pool.

If a virtual machine has any associated snapshots, deleting a virtual machine does not delete the

volumes associated with virtual machine VDIs. When the last available snapshot associated with the

virtual machine is deleted, the parent volume gets deleted as well.

Delete a Snapshot

When a snapshot of a virtual machine is deleted or uninstalled, the corresponding snapshots of all

volumes (on PS Series) for VM VDIs are deleted from the PS Series Group. To delete or uninstall a

snapshot, click on the template corresponding to the snapshot and select Uninstall Template.


Using PS Series replication with

XenServer Portable SRs

XenServer 5.0 introduces the concept of Portable Storage Repositories (Portable SRs). Portable SRs

contain all of the information necessary to recreate all the Virtual Machines (VMs) with Virtual Disk

Images (VDIs) stored on the SR after re-attaching the SR to a different host or pool. Portable SRs can

be used when regular maintenance or disaster recovery requires manually moving a SR between pools

or standalone hosts.

Portable SRs work by creating a dedicated metadata VDI within the specified SR. The metadata VDI

is used to store copies of the pool or host database as well as the metadata describing each VM’s

configuration. As a result the SR becomes fully self-contained, or portable, allowing it to be detached

from one host and re-attached to another as a new SR. Once the SR is re-attached, a restore process

is used to recreate all of the VMs on the SR from the metadata VDI.

For disaster recovery the metadata backup can be scheduled to run regularly to ensure that the

metadata SR is current. For more information on XenServer 5.0 portable SRs and restrictions on

usage, refer to the XenServer 5.0 Reference Manual.

Using replication for SR of type LVM over iSCSI

When using replication to protect storage repositories of type LVM over iSCSI, one needs to configure

replication for volumes backing the SRs.

1. Configure a replication partner (secondary) group for the primary PS Series group.

2. Configure replication for the appropriate SR volume(s). Replication schedules to create replicas at

specific intervals can be created for the volumes accessible to XenServer hosts.

3. On the primary XenServer host or pool, use the pool master console interface to schedule VM

metadata backup on the protected Storage Repository. Make sure that replication is configured for

the SR that holds pool or host metadata.

Note: For suspended VMs, please make sure to replicate the designated suspend SR.

On the secondary site, the replicas may be used to perform backup operations or for disaster recovery

operations should the primary site becomes unavailable. In order to attach the SR on XenServer host/

pool on the secondary site:

1. Once the replicas for the replicated SR volume are in the Ready state, promote the replica as

a volume or create a replica clone. Note that by default, replica clones have thin provisioning


2. For the replica clone, add appropriate access control records for XenServer hosts on the

secondary site to access the SR volume(s). For shared SRs, make sure to enable shared access

for the SR volume(s).

3. On the XenServer host or pool master on the secondary site, attach the replica clone or promoted

volume as an existing SR.

4. Using the Restore Virtual Machine Metadata option from XenServer local console, restore the VM

metadata to recover all virtual machines on the replicated SR volume.


Using replication for SR of type Dell EqualLogic

Using replication with SRs of type Dell EqualLogic is little different from replication with SRs of type

LVM over iSCSI. Unlike LVM over iSCSI SRs were all VDIs reside on a single volume on PS Series

Group, each VDI for Dell EqualLogic SRs, is backed by its own volume on the PS Series Group.

Hence replication needs to be configured for the SR and all the associated VDI volumes.

For SR of type Dell EqualLogic, in order to recover VMs on the secondary site:

1. Configure a replication partner (secondary) group for the primary PS Series group.

2. On the primary XenServer host or pool, use the pool master console interface to schedule VM

metadata backup on a protected Storage Repository. This process will create a new 255MB

volume on the PS Series Group. This volume holds the pool and VM metadata.

3. Configure replication for the SR volume and all associated VDI volumes, including the metadata

VDI. Apart from creating one-time replicas, a replication schedule can also be created to create

replicas at specific time intervals for all replicated volumes.

On the secondary site, the replicas may be used to perform backup operations or for disaster recovery

operation if the primary site is unavailable. In order to attach the SR on the replication partner:

1. Once the replicas for the replicated SR volume are in the Ready state, create clones of the SR

volume and all VDI volumes, including the metadata VDI volume. Note that by default, replica

clones have thin provisioning enabled.

Note: When creating clones from replicas make sure than the name and description of each clone is set to be exactly same

as source volumes. Failure to do so will prevent the XenServer hosts in the secondary site to reattach the SR and automatically

recover the VMs using the metadata VDI.

Note: A temporary volume promoted, from a replica and with the ability to demote to a replica set has a name and description

different than source volume. Hence, recovering VMs using such temporary volumes at replication site is not feasible at this time.

2. For shared SRs, make sure to enable shared access for the SR and all VDI volumes. Access

control records for all volumes are automatically created by the XenServer EqualLogic Storage


3. On the XenServer host or pool master on the replication site, attach the replica clone as an

existing SR.

4. Using Restore Virtual Machine Metadata option from XenServer local console, restore the VM

metadata to recover all virtual machines on the replicated SR volume.


XenServer Dell Edition Documentation:

Dell EqualLogic PS Series Online help:

XenServer 5.0 User Documentation:

PS Series Array Network Performance Guidelines:

About Citrix

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Based in Fort Lauderdale, Florida, Citrix has offices in 22 countries and approximately 6,200 channel and alliance partners in more

than 100 countries. Annual revenue in 2007 was $1.4 billion.

About Dell

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