In almost every situation,
storage virtualization is implemented as
software running on a hardware platform. This is true for
host-based virtualization where software is installed on an
available server; for dedicated appliances where the software
and dedicated server hardware are sold as a package; and for
fabric-based virtualization where software runs on a
switch. Still, the choice of hardware plays
a crucial role in virtualization, so users must understand the
capabilities and limitations of hardware deployment. Now that
you've reviewed the
essential issues involved in any virtualization
product, this guide focuses on the specific considerations
of virtualization hardware. You'll also find a series of
specifications to help make on-the-spot product comparisons
between vendors like Acopia Networks Inc., BlueArc Corp.,
EqualLogic Inc., Hitachi Data Systems Inc.and LeftHand Networks
Inc., and see suitable switch offerings from Cisco Systems Inc.,
Brocade Communications Systems Inc. and others.
@29123 Consider the modes of deployment. Host and
appliance-based storage virtualization is typically installed
in-band or out-of-band, while fabric-based virtualization is
implemented in storage area network
(SAN) switches. There are advantages and
disadvantages to each approach. In-band deployments actually sit
in the active data stream to handle virtualization. This is
often the most straightforward approach and requires no software
agents to collect and process information, but the presence of a
virtualization server in the data path can easily become a
traffic bottleneck. Out-of-band virtualization uses servers or
appliances that sit on the network but not directly in the data
path. This will not impair traffic performance but often
requires agent software installed on each platform being
virtualized -- increasing the maintenance burden for IT staff.
Implementing virtualization within the fabric is increasingly
popular because of the good performance, broad interoperability
and centralized management potential achieved through
intelligent switches.
Ensure that the hardware and software support each other.
This is not an issue for array-based or appliance-based
virtualization where the hardware and software have already been
mated for you. This is a critical concern with host-based and
fabric-based virtualization where you need to choose compatible
platforms. For example, you might select a Cisco MDS9000 SSM to run
EMC Corp.'s Invista software in the switch. Server and switch
hardware must meet the software's requirements and provide enough
processing headroom to accommodate some amount of scaling into the
future.
Consider the connectivity and protocol support. When
evaluating hardware, it's also important to determine how it will
actually connect to your local area network (LAN) or SAN and to
ensure that it supports the protocols currently being used by the
network. As an example, the FM5500 file manager from Attune Systems
Inc. offers ten 1 Gigabit Ethernet (GigE) ports. By comparison, the
iQ2280 storage system from iQStor provides four 4 Gbit Fibre
Channel (FC) ports. Protocol support can include
CIFS,
NFS,
TCP,
UDP,
SNMP and so on.
Upfront planning is essential. Virtualization should not
be attempted without a comprehensive deployment plan that addresses
hardware preparation, software installation, physical installation
and interconnection, setup and configuration, and testing. The
virtualization vendor can generally assist with these
considerations prior to purchase. Remember that physical
installation and subsequent setup will cause some downtime and
service interruptions for your users, so installation may be
reserved for evening or weekend hours. Have a fallback plan in
place, so that the virtualization can be removed or reversed if
unexpected problems arise.
Evaluate disruption levels. Upgrades and changes to
virtual storage assignments sometimes result in service disruptions
for users and applications. For example, an application may be
temporarily unavailable while allocated disk space is being
increased. An increasing number of storage virtualization products
are focusing on nondisruptive techniques for upgrades and changes.
The Maestro File Manager appliance from Attune is one product that
claims transparent upgrades, expansions and migrations. Use lab
testing to determine the actual disruptions that occur during file
server migrations, upgrades and other maintenance. Excessive
disruption may prompt you to select an alternate product.
Consider the security features. Your virtualization
platforms should always be protected by security features, such as
usernames and passwords or other forms of authentication, such as
Kerberos. Products like the V-Switch 3800 from Sanrad Inc. supports
ACLs, SRP,
RADIUS and iSNS. Security features protect
data within the SAN and prevent unauthorized changes to storage
allocation or service levels -- especially in the fabric where
switching can impact all network traffic. Evaluate the security
features of your virtualization product and be sure to
proactively implement security. Part of any security should also
include a comprehensive change policy to help storage
administrators prioritize and manage changes to virtual storage
resources.
Evaluate performance and latency. Virtualization
platforms can sometimes experience latency when accessing
directories -- especially directories with many small files. Some
virtualization products attempt to compensate for this latency by
using file acceleration techniques. Others may handle performance
issues using tactics like volume rebalancing and migrating lightly
used files to other storage resources on a lower tier or another
virtual volume with lower utilization. Ultimately, it's important
to test any virtualization system and see how it performs under
actual load conditions.
The virtualization hardware product specifications page in this
chapter covers the following products:
- Acopia Networks Inc.; Adaptive Resource Switch (ARX)
switch
- Cisco Systems Inc.; MDS 9000 IP Storage Services Module
(SSM)
- EqualLogic Inc.; PS Series Storage Arrays
- FalconStor Software Inc.; (IPStor) NSS appliances (Models 310
and 350)
- Fujitsu Computer Systems Corp.; ETERNUS VS900
- Hitachi Data Systems Inc.; TagmaStore Universal Storage
Platform 1100
- Network Appliance Inc.; V-Series appliances
- OnStor Inc.; Bobcat Series NAS Gateway & Pantera Clustered
NAS
- Reldata Inc.; IP Storage Gateway 9240
- Sanrad Inc.; V-Switch 3800
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