Storage virtualisation is touted as green, money-saving and a great help to storage administrators, but Dr Kevin McIsaac of analyst firm IBRS says that Thin Provisioining - not virtualisation - will be a more important part of storage appliances in the near future.
McIsaac describes storage virtualisation as “poorly defined, poorly understood and not widely used,” adding that “Infrastructure managers must understand the realities of storage virtualisation, learn to separate vendor hype from facts, and discover where it can be applied to give real benefits.”
McIsaac believes thin provisioning is the clear alternative.
What is thin provisioning?
Traditional provisioning of disk space has seen each application allocated a certain amount of storage in an array. Provisioning is not a trivial task and is important to get right, because storage space allocated to one application is nearly always inaccessible to others.
That exclusivity of access means administrators tend to be very conservative when they provision an array. Many will therefore decide that an application which regularly uses 50GB of storage should have 200GB of capacity provisioned to make sure it has plenty of overhead available in case of surges.
This practise, while commendably far-sighted, has the unfortunate effect of locking away 150GB of storage capacity for a rainy day, rather than making that capacity available for other applications.
Thin provisioning does away with this waste by allowing administrators to over-provision for their applications. This has three benefits.
The first is that, according to Ovum storage analyst Tim Stammers, “it doubles the capacity of every piece of storage you buy.”
Another is that operators of several applications can over-provision them all, safe in the knowledge that thin provisioning does all the juggling required to indentify and utilise the spare capacity in each application’s allocation of storage.
The other is that users need only provision an application once, even if they have less physical storage than they provision. This trick makes it possible to provision an application to use 500GB, even though a storage array only contains 250GB. As the application nears the physical capacity of the array, more storage can be added without needing to perform additional administration chores.
“While thin provisioning is not yet widely used, its adoption will accelerate rapidly as vendor support widens and more storage administrators become aware of its benefits,” McIsaac says. “Over the next 18 it will become as pervasive as other array-based virtualisation features such as RAID and snapshots.”
McIsaac’s prediction is already coming true. HDS and Dell EqualLogic have both brought the technology to market, and NetApp plans to do likewise. EMC has pledged to bring the technology to all of its arrays.