HP XP P9500 Storage - Manual (Page 38)

If a path in which an error has occurred recovers from the error, HDLM can
then switch back to that path. This is called a failback.
Two types of failovers and failbacks are available:
• Automatic failovers and failbacks
• Manual failovers and failbacks
Failovers and failbacks switch which path is being used and also change the
statuses of the paths. A path status is either online or offline. An online status
means that the path can receive I/Os. On the other hand, an offline status
means that the path cannot receive I/Os. A path will go into the offline status
for the following reasons:
• An error occurred on the path.
• A user executed the HDLM command's offline operation.
For details on the offline operation, see
offline (Places Paths Offline) on
page 6-6 .
For details on path statuses and the transitions of those statuses, see Path
Status Transition on page 2-19 .
Notes
Switching a reserved path might take several seconds. A reserved path is
switched in the following cases:
¢
The reserved path is placed offline.
¢
An owner path is placed online when a path has been reserved while
only non-owner paths are online.
Automatic Path Switching
This section describes the automatic failover and automatic failback functions
that automatically switch paths.
Automatic Failovers
If you detect an error in a path being used, you can keep operating the
system by changing the path state to offline, and using other online paths.
This function is called automatic failover. Automatic failovers can be used for
the following levels of errors:
Critical
A fatal error that might stop the system.
Error
A high-risk error, which can be avoided by performing a failover or some
other countermeasure.
For details on error levels, see Filtering of Error Information on page 2-32 .
When the Thunder 9500V series, or Hitachi AMS/WMS series is being used,
HDLM will select the path to be used next from among the various paths that
access the same LU, starting with owner paths, and then non-owner paths.
2-16
HDLM Functions
Hitachi Dynamic Link Manager User Guide for Solaris ®