HP StorageWorks SAN Virtualization Services Platform Best Practices Guide (5697-0935, May 2011)

Capacity pools
Figure 11 (page 25) shows how back-end LUs are grouped into a capacity pool and then made
into SVSP virtual disks. The back-end LUs must be a minimum of 1 GB in size to be seen by SVSP,
and no larger than 2 TB. Once the virtual disks are created, they can be presented to one or more
hosts.
Figure 11 Virtual disk creation
TIP: SVSP field experience indicates that storage pools should have a minimum of 8 physical
LUs with 16 physical LUs being optimal. More LUs in each storage pool are allowed and in some
cases may be desirable if other scalability limits are not exceeded. Less than 16 LUs in each storage
pool will work, but is discouraged for performance reasons. A single LU in a pool is not supported
for advanced services.
Although you can create a storage pool from two storage arrays, HP recommends that you use
one array, making it easier to isolate problems and monitor performance.
Keeping storage pools simple, or at least keeping them as simple as possible while meeting the
needs of the applications that will be using the virtual disks from the pool is recommended.
Larger numbers of virtual disks for a capacity pool provide more opportunities to distribute the
workload across multiple array ports, however there are trade-offs involved. One trade-off of this
simple general-purpose pool construction approach is that it uses back-end LUs and back-end paths
in quantities that can run out before achieving the maximum capacity or the maximum number of
arrays supported by SVSP. In other words, to achieve SVSP maximums it is necessary for all
back-end LUs to be the maximum size and the number of paths from the back-end array be kept
to a minimum. (See the current release notes for SVSP maximums.)
Performance pools
Performance pools can significantly improve performance and rarely degrade performance. If the
I/O stream is largely transactional, a performance pool will typically perform better than a capacity
pool. When considering sequential streams, realize that multiple sequential streams often act as
a transactional stream. Note that a single stream sequential I/O to a single virtual disk may perform
better with a capacity pool rather than a stripe pool. Monitor the array performance to confirm
that the I/O stream has not created a hot spot on a disk.
Capacity pools 25