SANs tuned for virtualisation

Virtualisation is moving further into the data centre all the time, with even critical large scale applications like Exchange and databases now being virtualised. Whether you're using virtualisation to make large applications more manageable or to consolidate many small applications, a server with lots of RAM, lots of processor cores, and lots of I/O is a good thing. And so is a SAN packed with features that ease the management of storage for virtual machines.

From a storage viewpoint, each virtual machine uses a file to simulate a physical hard disk. This file, a VMDK (Virtual Machine Disk Format) under VMware or VHD (Virtual Hard Disk) under Microsoft, can be located on a server's internal drive or on a SAN. There are several advantages to putting the file on a SAN: The file can be duplicated using the storage's snapshot function, the file can be moved easily from one hardware server to another for scalability or fault tolerance, and the storage itself can be more easily made fault tolerant.

I tested five midrange SAN systems that deliver the goods for virtual environments: the Compellent Storage Center 4.0, the Dell EqualLogic PS4000, the HP StorageWorks 2000sa G2 Modular Smart Array, the Pillar Axiom 600 from Pillar Data Systems, and a build it yourself pairing of the Promise vTrak E610f hardware and DataCore's SANmelody 3.0 storage software.

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The prices (as tested) of these systems range widely, from less than £6,000 for the Promise Technologies and DataCore combination to £80,000 for the Pillar Data system. All the manufacturers have models ranging from inexpensive starters to very high performance datacentre ready systems. As you can tell from the range in price, the models I tested don't necessarily compete with each other.