Manual Path Switching - Hitachi XP P9500 User Manual

Automatic Failbacks
When a path recovers from an error, HDLM can automatically place the
recovered path back online. This function is called the automatic failback
function.
When using the Hitachi AMS/WMS series, HDLM will select the next path to be
used first from among the online owner paths, and then from the online non-
owner paths. As a result, if an owner path recovers from an error, and then
HDLM automatically places the recovered path online while a non-owner path
is in use, the path will be automatically switched over from the non-owner
path to the owner path that just recovered from the error.
When the Universal Storage Platform V/VM, Virtual Storage Platform, Hitachi
AMS2000 series, or Hitachi SMS is being used, all the paths are owner paths.
As a result, if the path that was previously used recovers from an error, and
then HDLM automatically places the recovered path online, the path that is
currently being used will continue to be used (as opposed to switching over to
the path that was just recovered).
When an intermittent error
places the path offline and then online again, which can cause I/O
performance to drop. In this case, we recommend that you configure
intermittent error monitoring to exclude paths with intermittent errors from
the automatic failback process.
Automatic failback is implemented by functionality provided by VMware
vSphere ESXi, and cannot be disabled.
Intermittent error monitoring can be specified in the HDLM command's set
operation. For details on the set operation, see
Environment) on page
#
An intermittent error means an error that occurs irregularly because of
some reason such as a loose cable connection.

Manual Path Switching

You can switch the status of a path by manually placing the path online or
offline. Manually switching a path is useful, for example, when system
maintenance needs to be done.
You can manually place a path online or offline by doing the following:
• Execute the dlnkmgr command's online or offline operation.
For details on the online operation, see
page
Paths Offline) on page
However, if there is only one online path for a particular LU, that path cannot
be manually switched offline. Also, a path with an error that has not been
recovered from yet cannot be switched online.
#
6-15.
6-11. For details on the offline operation, see
6-7.
HDLM Functions
Hitachi Dynamic Link Manager User Guide (for VMware(R))
occurs in a path, automatic failback repeatedly
set (Sets Up the Operating
online (Places Paths Online) on
offline (Places
2-13