HP StorageWorks External Storage XP user guide (T1706-96006, June 2006)

External Storage XP user guide 153
HP StorageWorks Command View XP user guide for XP Disk Arrays or the HP StorageWorks XP Remote
Web console user guide for XP12000/XP10000/SVS200.
Recommendations
Performance considerations for using EVAs as external storage
Unlike the MSA family of 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/XP10000/SVS200 external port to a given EVA controller (remembering
that the EVA3000/5000 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/XP10000/SVS200 external port versus the benefit of any added EVA external
storage performance. For firmware revisions specified in ”Preface” on page 147, a host-connected EVA
port can out-perform an external storage-connected XP12000/XP10000/SVS200 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/XP10000/SVS200 external ports to dedicate to accessing an attached EVA.
Defining alternate paths
The XP12000/XP10000/SVS200 supports up to eight defined Fibre Channel paths to an external
storage LDEV. HP recommends verifying that each EVA3000/5000-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 82 illustrates this step.
Figure 82 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/XP10000/SVS200 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.