Hitachi Dynamic Provisioning without Thin Provisioning

Hitachi Dynamic Provisioning, HDP, is a feature of the USP V/VM which does virtualization of storage capacity in a pool of storage consisting of multiple RAID array groups. This pool of physical RAID array groups is divided up into 42 MB pages and used on-demand by any of the virtual host volumes using the pool. This enables HDP to provide a number of services.

The first benefit of HDP that everyone thinks of is thin provisioning. Thin Provisioning enables the USP V/VM to fill a request for a LUN allocation, for example 100 GB, with virtual capacity, and thinly provision the LUN with 42 MB pages of real storage capacity as the application starts to write to it. The unused capacity for the 100GB LUN allocation is then available to be used to thinly provision other LUN allocation requests from the same HDP pool. This helps to increase the utilization of storage by eliminating most of the allocated but unused portion of a LUN.

However, the real reason Hitachi calls this feature Dynamic Provisioning is that it does just that. It enables IT to dynamically provision LUNs from this HDP pool by assigning virtual LUN capacity as quickly as drag and drop. Instead of taking hours to provision a new server with LUNs, HDP can dynamically provision a new server in a matter of minutes.

Another service is thin moves and copies. Since HDP know how many pages are assigned to a LUN allocation when it does a move or copy of that LUN, it only moves or copies the actual used pages and not the whole LUN. This reduces operational expense by eliminating the moving or copying of unused capacity.

Since we wide stripe the LUN by using multiple 42 MB pages which in turn use disk spindles across the whole HDP pool, we can increase throughput and decrease response time by employing more disk spindles in the performance of the I/O requests to all the virtual volumes. So wide stripe performance is another benefit.

One large storage user has decided to use HDP but not use thin provisioning. He does not want to run the risk of over subscribing his storage under peak conditions, so he never allocates more capacity than he physically has in the HPD pool. So what is the benefit of this if he is not using thin provisioning?

1. He still gets the benefit of dynamic provisioning, the ability to provision new servers in a matter of minutes.
2. He also has the operational benefit of thin moves and copies. For instance, it takes less time to replicate 42 MB of used capacity than 100GB of allocated capacity.
3. And he still has the performance benefits of wide striping. This equates to eliminating storage performance hot-spots which in the past kept administrators needlessly busy moving application data around the array.

His view is that capacity is cheap and getting cheaper, but his operational expenses are going to continue to increase. So the benefit he sees in HDP is not in thin provisioning but in dynamic provisioning, thin copies and moves, and wide stripe performance.

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