Manual Path Switching - Hitachi XP P9500 User Manual

In order to use the automatic failback function, HDLM must already be
monitoring error recovery on a regular basis.
When using the Thunder 9500V series, or 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 Lightning 9900V series, Hitachi USP, Universal Storage Platform V/
VM, Virtual Storage Platform, Hitachi AMS2000 series, or Hitachi SMS is being
used, all the paths are owner paths. Therefore, if an owner path recovers
from an error and HDLM automatically places the recovered path online, the
path to use is not switched.
When intermittent errors
failback function, the path status might frequently alternate between the
online and offline statuses. In such a case, because the performance of I/Os
will most likely decrease, if there are particular paths in which intermittent
errors might be occurring, we recommend that you set up intermittent error
monitoring so you can detect these paths, and then remove them from those
subject to automatic failbacks.
You can specify the automatic failback function or intermittent error by the
dlnkmgr command's set operation. For details on the set operation, see
(Sets Up the Operating 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.
HDLM uses the same algorithms to select the path that will be used next,
regardless of whether automatic or manual path switching is used.
When using the Thunder 9500V series, or Hitachi AMS/WMS series, HDLM
selects the switching destination path from owner paths and then from non-
2-18
#
occur on paths and you are using the automatic
6-11. For details on the offline operation, see
6-6.
HDLM Functions
Hitachi Dynamic Link Manager User Guide (for AIX(R))
6-16.
online (Places Paths Online) on
offline (Places
set