Server and desktop virtualisation is no longer the preserve of large organisations.
SMEs are virtualising apace, and that means they need scalable and flexible storage. That means shared storage, and to satisfy that need a number of vendors offer entry-level SAN systems targeted at the SME market.
In this article we survey the key attributes to expect from entry-level SAN products and take a look at products from some key vendors in the space.
Why SAN for SME storage?
NAS appliances can offer reliable storage for virtual machines but fall over when an organisation needs to host data that requires direct block storage access such as for databases. The ability to manipulate block sizes for maximum storage efficiency combined with a dedicated network transport architecture in a SAN environment introduce levels of flexibility and reliability to host flexible virtual server estates which NAS is unable to provide.
What defines entry level SAN?
The distinction between SAN and NAS has become blurred in the SME market with many NAS appliances now offering some SAN features, namely block access to data, usually via iSCSI.
So, for the purposes of this discussion we’ll focus on products that major in providing block access to data. First of all, let’s look at the type of features to expect in entry-level SAN products.
Regardless of size, every organisation with a virtualised server or desktop environment requires resilience and reliability from their systems. With that in mind even small scale SAN implementations often offer multi-controller failover protection and redundant network connectivity at reasonable cost.
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The advent of high bandwidth Ethernet networking combined with the widely adopted iSCSI storage transport protocol have removed the cost barrier traditionally imposed by Fibre Channel-based SAN networking.
Multi-port network connectivity is now a standard feature in entry level SANs and combined with native VLAN capability in Ethernet switches it is now possible to mimic the behaviour of Fibre Channel zones in Ethernet environments thereby further enhancing data transport quality of service.
Disk type options have also significantly increased. The widespread adoption of SATA, SAS and SSD has reduced costs and introduced performance capabilities previously impossible outside enterprise-level arrays.
With data densities of up to 3TB available in a single SAS disk for lower tier storage and SSD performance now vastly outstripping that of 15,000rpm Fibre Channel drives for tier 1, entry-level SANs are now able to provide a range of disk performance options previously limited to the enterprise.
Many entry-level SAN products also now attract virtualisation vendor accreditations designed to provide technical confidence to organisations looking to adopt virtualisation technology. The main examples of this are the VMware Ready and Microsoft Hyper-V certification programme.
Entry-level SAN products
The Overland SnapSAN S1000 is an entry-level SAN with iSCSI connectivity (and Fibre Channel SAN and SAS as direct-attached storage options). The base unit comes with a minimum of four drives (SAS and nearline-SAS) and is Microsoft and VMware certified. Ports are 8 x 1 Gbps Ethernet or 4 x 10 Gbps Ethernet per two controllers depending upon the option chosen. Up to 12 drives of up to 3TB capacity can be housed in the baseline S1000. It comes with a single controller or optional dual controllers with active-active failover capabilities and mirrored cache. RAID configuration features include RAID levels 0, 1, 0+1, 3, 5, 6, 10, 30, 50, 60 and include the ability to create up to 1,024 total logical volumes. Management features include global and dedicated hot spare disks, write-through or write-back caching, online disk roaming, online volume expansion, online RAID migration and volume cloning. The S1000 can be expanded up to a total of 60 drives with four Snap E1000 expansion units.
Even small scale SAN implementations often offer multi-controller failover protection
Infortrend offers an entry-level SAN subsystem, the ESVA E10-2130 iSCSI, which comes with dual controllers and a maximum of 16 drives per base system with optional scale-out expansion to 64 drives. It offers four 1 Gbps Ethernet ports and drive types supported include 2.5” and 3.5” SAS and SATA plus SAS SSD. The E10-2130 is VMware Ready and Microsoft Hyper-V certified. Storage features on the product include storage pooling, thin provisioning, automatic data migration, prioritised volume accessibility, distributed load balancing and automated storage tiering. RAID levels 0, 1, 3, 5, 6 are supported and there are a wide range of data protection features including local snapshots, volume copy and mirror features, and synchronous or asynchronous replication.
The B1200i from Drobo is an iSCSI-based entry-level SAN product that comes as an unpopulated twelve-bay unit that can be filled with SAS or SATA drives (you can’t mix them in one unit) and has SSD as an option too. It has dual power supplies but not dual controllers as standard. Three 1 Gbps Ethernet ports provide iSCSI network connectivity in addition to a dedicated unit management network port. You can’t add a capacity expansion unit, but Drobo’s BeyondRAID technology enables different drive capacities to be swapped in the unit so allows for continuous expansion as larger capacity drives become available. Storage features of the B1200i include thin provisioning, instant volume expansion, mixed drive size utilisation and automatic data tiering. Full support for Microsoft and VMware virtualisation environments is provided.
Qsan’s AegisSAN range offers a variety of iSCSI (and Fibre Channel) configurations aimed at the SME market in a dual controller format. Its P500Q arrays offer 2 x 10 Gbps Ethernet ports per controller while the P300Q has 4 x 1 Gbps Ethernet ports per controller. The P500Q and P300Q come in form factor/capacity options that range from 2U/12 drive to 4U/24 drive with expansion possible up to 72 drives. RAID levels 0, 1, 0+1, 3, 5, 6, 10, 30, 50 and 60 are supported with up to 1,024 total logical volumes which can be shared concurrently by up to 16 separate hosts. Features include snapshots, N-way mirroring, disk spin-down and virtualisation support for VMware, Microsoft and Citrix.
Dothill aims its AssuredSAN 2322 and 2332 iSCSI arrays at the entry-level SAN market. The 2322 features 24 x 2.5” drive capacity with SAS, SATA and SSD drive options while the 2332 features a 12-drive capacity array for 3.5” drives. Both systems are expandable by adding JBOD enclosures and can scale to 96 disks, although the 2332 requires an extra chassis to achieve this due to the larger disk format. High availability features include redundant hot-swap controllers, multi-pathing support and volume snapshots. RAID levels supported include 0, 1, 3, 5, 6, 10 and 50 and 1 GB iSCSI connectivity is offered via four dedicated ports. Dothill’s dual cache mirroring is capacitor- rather than battery-powered and so eliminates battery replacement issues.