Manual path switching, Manual path switching -21 – HP XP P9500 Storage User Manual
Page 43
When intermittent errors
#
occur on paths and you are using the automatic
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 6-14
.
#
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
online (Places Paths Online) on
. For details on the offline operation, see
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 will
select the next path to be used first from among the online owner paths, and
then from the online non-owner paths. When the Lightning 9900 series,
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 that access the same LU as the path that is currently being used
are candidates for the switching destination path.
Executing the online operation places the offline path online. For details on
the online operation, see
online (Places Paths Online) on page 6-10
. After a
path status is changed to online, the path can be selected as a useable path
by HDLM in the same manner as automatic path switching. When using the
Thunder 9500V series, or Hitachi AMS/WMS series, HDLM selects the path to
use from online owner paths, and then from online non-owner paths. When
the Lightning 9900 series, Lightning 9900V series, Hitachi USP, Universal
Storage Platform V/VM, Virtual Storage Platform, Hitachi AMS2000 series, or
Hitachi SMS is being used, since all the paths are owner paths, the path to
HDLM Functions
2-21
Hitachi Dynamic Link Manager User Guide (for Linux(R))