Recommendations; Performance Considerations For Using Evas As External Storage; Defining Alternate Paths - HP StorageWorks User Manual

XP12000-attached host, see the HP StorageWorks Command View XP user guide for XP Disk Arrays or the
HP StorageWorks XP Remote Web console user guide for XP12000/XP10000.

Recommendations

Performance considerations for using EVAs as external storage

Unlike the MSA family of disk arrays, an EVA can be configured to perform I/O operations with both its
controllers on separate EVA LUs simultaneously (Active/Passive capability). Therefore, it is possible to
realize more/better performance from an EVA in an external storage role by creating multiple connections
from the XP12000 external port to a given EVA controller (remembering that the EVA GL models have two
ports per controller) than a similar configuration with an MSA (only one port per controller). In spite of this,
HP strongly cautions you to carefully weigh the financial cost of a dedicated XP12000 external port versus
the benefit of any added EVA external storage performance. For firmware revisions specified in "Preface"
on page 119, a host-connected EVA port can out-perform an external storage-connected XP12000
external port by an estimated ratio of as much as 4 to1 when the number of usable I/O operations per
second (IOPS) is considered. It is for this reason that you must be careful when choosing the number of
XP12000 external ports to dedicate to accessing an attached EVA. For more information about XP external
storage's performance characteristics, see

Defining alternate paths

The XP12000 supports up to eight defined fibre channel paths to an external storage LDEV.
HP recommends verifying that each EVA GL-resident external storage LDEV has at least one alternate path
to the controller to which it does not have a preferred path assigned. If additional redundancy is desired,
configure more paths. These paths, however, are not used for I/O unless a fault occurs and the EVA is
forced to failover to these paths. Use Command View XP or XP Remote Web Console to verify and
configure external storage LDEV paths. On the LU Operation pane in External Storage, right-click on an
external LU, and select Path Settings. The Path Setting pane appears. Right-click on the undefined paths in
the Alternate Paths list, and select Add Path.
Figure 63 Configuring alternate paths
In addition to adding and deleting paths, use this pane to change a path's priority. Right-click on the path,
and select Priority Up or Priority Down.
For failover operations, the XP12000 attempts to fail between defined paths to a given external LDEV
provided that it does not encounter another previously active (prior to path fault) path. Unlike the MSA,
failback operations for EVA-resident external LDEVs is automatic.
126 Using XP12000 disk arrays with EVA GL disk arrays attached as subordinated external storage disk arrays
"External Storage XP for the
Figure 63 illustrates this step.
XP12000/XP10000" on page 13.