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

of these large disk groups. Contrast this with the HP XP array that allows for either a 4- or 8-member
disk group for RAID1. RAID5 groups on the HP XP array can be built from 4, 8, 16, or 32 spindles.
The number of array ports influences the number of paths available to SVSP for communicating
with the back-end LUs. Using multiple ports affects performance as well as availability. See “Array
configuration” (page 18) for more information.
The array controllers determine the potential performance capacity (I/O handling capacity) available
from a given collection of back-end LUs. Keep array resource utilization below 80% of the total
potential capacity – even less for initial implementation to allow for growth.
Be sure you choose arrays that can provide the right storage for your business needs, storage that:
• Can achieve your availability and reliability goals
• Has the capacity to achieve predictable application performance
• Has the flexibility to expand with ease
• Permits ease of debugging and troubleshooting
Consult with the array vendor to help you consider all the advanced features of the array and how
they can affect your choices when building back-end LUs.
Selecting back-end LUs for a storage pool
To achieve predictable and consistent performance, as well as ease of troubleshooting, do not mix
RAID levels, spindle speeds, and array types (or arrays) in a storage pool. To a lesser extent, disk
types (with the exception of FATA) and disk sizes should be consistent in the pool. Again, while it
is possible to have heterogeneous pools created from multiple arrays and different characteristics,
more oversight must be undertaken to avoid problems, and problems may take a bit of
troubleshooting to resolve.
CAUTION: Once a back-end logical unit is added to a storage pool, do not change any of its
characteristics such as logical unit number or size. Never manage the SVSP back-end virtual disks
directly from the array management interface without first removing them from SVSP. The procedure
is documented in the HP StorageWorks SAN Virtualization Services Platform Administrator Guide.
Pool size considerations
Whether it is better to build small storage pools or large pools, each has its advantages. Having
fewer, large pools are easier to manage, and since the pool free space in the same pool is used
for snapshot, asynchronous mirrors, and thin provisioning, there is less likelihood of stranded
capacity. However, small pools may allow the administrator to better partition the storage for
various user groups or to have a pool per back-end array to ease troubleshooting.
Alerts are set up on pool capacity; small pools or large pools may influence the alert management
options.
When building the storage pools, plan for future pool expansion. SVSP virtual disks are carved
from the storage pool and then served to hosts. If that SVSP virtual disk needs to expand, there
must be room in the pool to support this growth. Pools can be expanded by adding additional
back-end LUs. But this means that you need to have the additional capacity on the storage array
to create new back-end LUs to present to the SVSP.
FATA drives
Fibre Attached Technology Adapted (FATA) drives are significantly slower and have a shorter duty
cycle than their Enterprise-class Fibre Channel counterparts. This should be considered when
creating pools. It should also be noted that creating synchronous mirrors between a Fibre Channel
pool and a FATA pool will result in performance below the normal FATA drive performance.
24 Storage pools