The Virtualization Room

Jan 23 2012   3:49PM GMT

VMware VSA capacity increases with new RAID requirements

Beth Pariseau Beth Pariseau Profile: Beth Pariseau

The vSphere Storage Appliance (VSA) released with vSphere 5 now supports more usable capacity per host thanks to relaxed RAID requirements, according to a VMware blog post.

RAID, or Random Array of Independent Disks, refers to the way data is striped and / or mirrored across disks to achieve redundancy. Higher RAID levels afford better data protection, but can eat up more disk capacity. Previously, the VSA required RAID 10, which offers high levels of data protection, but contributed to a 75% capacity overhead for the overall VSA.

Now, the VSA supports RAID 5 or RAID 6, which use fewer disks for data protection, resulting in more available capacity for users.

Under RAID 10, hosts in a three-node VSA cluster running the maximum eight disks at the maximum 2 terabytes (TB) capacity each would have a raw capacity of 16 TB, but a usable capacity of just 4 TB. Across the entire cluster, this means that 48 TB raw capacity would be needed to yield 12 TB of usable space.

VMware’s VSA documentation now contains a capacity calculator showing the new capacities available with the new RAID levels. Long story short, the same maximum configuration of eight 2 TB disks per host in a three node cluster now yields 21 TB in a RAID 5 configuration and 18 TB in a RAID 6 configuration.

High storage overhead was among the chief complaints about the VSA after its launch last August. The relaxed RAID requirements do not address other areas of criticism about the product, such as the fact that users must choose between a two and a three-node cluster before provisioning; the VSA cannot start as a two-node configuration and scale up to a three-node configuration.

“While this makes the VSA more functional by increasing the capacity of the storage, I still see it as a ‘niche’ player,” wrote Tim Antonowicz, senior architect at Salem, NH-based VAR Mosaic Technology, in an email. “There aren’t many scenarios where the VSA will be a better play than a dedicated SAN…as for our customers that were looking at deploying the VSA, we have been able to move them into a low-cost SAN solution for similar pricing and they have gone that route instead of using the VSA.”

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