HP StorageWorks XP Remote Web Console Software - Manual (Page 101)

External Storage XP user guide 101
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 91, 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 ” External Storage XP for the XP10000/XP12000 ” on page 11.
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 61 illustrates this step.
Figure 61 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.
Troubleshooting
• Be careful to define an external storage LDEV presented to the XP12000 by the EVA from the EVA
controller that is presently serving its associated LU in an active status.
• If you attempt to define an LDEV from an LU via that LU’s passive controller, the resulting external
storage LDEV is placed in a blockade state.