HP XP P9500 Storage - Manual (Page 40)

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.
In order to use the automatic failback function, HDLM must already be
monitoring error recovery on a regular basis.
When the Thunder 9500V series, or Hitachi AMS/WMS series is being used,
HDLM selects the path to use from online owner paths, and then from online
non-owner paths. Therefore, if an owner path recovers from an error and
HDLM automatically places the recovered path online while any non-owner
path is in use, the path in use will be switched to the recovered owner path.
When the Lightning 9900 Series, Lightning 9900V Series, Hitachi USP Series,
Universal Storage Platform V/VM Series, Virtual Storage Platform Series,
Hitachi AMS2000 Series
#1 , Hitachi SMS Series #1 , HUS100 Series #1 , or HUS
VM 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 in use will not be switched to the recovered owner path.
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
monitoring by the dlnkmgr command's set operation. For details on the set
operation, see set (Sets Up the Operating Environment) on page 6-17 .
#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,
for example, 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 6-11 . For details on the offline operation, see offline (Places
Paths Offline) on page 6-6 .
2-18
HDLM Functions
Hitachi Dynamic Link Manager User Guide for Solaris ®