Hitachi Dynamic Link Manager Software Users Guide for Linux

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 series, Universal Storage
Platform V/VM series, Virtual Storage Platform series, VSP G1000 series,
Hitachi AMS2000 series
#1
, Hitachi SMS series
#1
, HUS100 series
#1
, or HUS
VM 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 intermittent errors
#2
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
set
(Sets Up the Operating Environment) on page 6-15.
#1
This storage system applies when the dynamic I/O path control function is
disabled.
#2
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
page 6-10. For details on the offline operation, see offline (Places
Paths Offline) on page 6-6.
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.
HDLM Functions
2-21
Hitachi Dynamic Link Manager (for Linux®) User Guide