HP StorageWorks SAN Virtualization Services Platform administrator guide (5697-0204, January 2010)

to get it out of that state. If ISLs are being used, it is best practice to set up alert levels in the switches
to ensure that notification of problems are realized.
Limit the number of switch hops from the servers to the DPMs, and from the DPMs to the storage, to
a maximum of three hops. In no case should the server-to-storage route exceed a total of seven switch
hops.
Mixing SAN-level virtualization with non-virtualized environments
Environments in which some logical units (LUs) are accessed directly from the array and other LUs are
accessed by the SVSP DPMs are supported. The same back-end LU must not be presented to the SVSP
and directly to servers, or data corruption will occur. Naming conventions that help distinguish between
these two presentations is one way to make it easier to avoid and troubleshoot this kind of problem.
Setup volume configuration
SVSP field experience has shown that many issues arise when access to SVSP setup volumes is slow.
SVSP version 3 code contains new informational and warning messages for the setup volumes that
may be observed in the event viewer. The VSM event log must be monitored for messages indicating
slow setup volume updates.
If the event log indicates a recurring setup volume problem over several hours the following actions
should be taken:
• Verify that the setup volumes are made from similar performance-based storage.
• Verify that the volumes are made from high performance RAID1 storage.
• Verify that the arrays containing the setup volumes are not extremely loaded.
• Move the setup volumes to less busy or faster arrays.
• Move the setup volumes to their own disk group or volume group.
• Move some of the setup volumes to dedicated arrays.
• Reduce the number of setup volumes.
Configurations with large numbers of service-enabled volumes (for example, thin provisioned or with
PiTs) generate the most demand for setup volume access.
Setup volumes might be spread across different arrays for additional redundancy, but remember that
all writes are mirrored, and therefore the slowest performance volume will determine when the write
is acknowledged. HP does not recommend placing all three volumes on a single array; if that is all
that is available, create only two setup volumes and use different pools if the array has that option.
Building basic storage pools
Storage pools can be optimized for performance or for capacity; however, there is only one way to
configure storage pools to enable the maximum 2 PB per domain, and another way to deliver maximum
performance, but not both at the same time. This section defines the best practices for building
capacity-optimized storage pools.
Experience with SVSP in the field has indicated that pools should be built using at least 16 back-end
LUs. Adding more back-end LUs to a pool is allowed, and in some cases may be desirable, as long
as other scalability limits are not exceeded. Less than 16 LUs in each SVSP should also work, but is
discouraged because it limits the capabilities of the system to distribute the I/O across the many paths
to the storage.
Configuration best practices114