Automatic Path Switching; Automatic Failovers - Hitachi XP P9500 User Manual

• An error occurred on the path.
• A user executed the HDLM command's offline operation.
For details on the offline operation, see
page
For details on path statuses and the transitions of those statuses, see
status transition on page

Automatic path switching

The following describes the automatic failover and failback functions, which
automatically switch a path.

Automatic failovers

If you detect an error on the path that is currently being used, you can
continue to use the system by having the status of that path automatically
changed to offline, and then automatically have the system switch over to
another online path. This functionality is called automatic failover. Automatic
failovers can be used for the following levels of errors:
Critical
A fatal error that might stop the system.
Error
A high-risk error, which can be avoided by performing a failover or some
other countermeasure.
For details on error levels, see
When the Thunder 9500V series, or Hitachi AMS/WMS series is being used,
HDLM will select the path to be used next from among the various paths that
access the same LU, starting with owner paths, and then non-owner paths.
For example, in
controller of an LU is CHA0, and access to the LU is made via only one path
(A). After that access path (A) is placed offline, the first choice for the
switching destination is the other path connected to CHA0 (B). If an error
also occurs on that path (B), then the next possibility for a path comes from
one of the two paths (C or D) connected to CHA1.
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. This means all the paths accessing the
same LU can be possible switching destinations. For example, in
Path switching on page
After the access path is placed offline, the switching destination is one of the
paths (B), (C), and (D).
For details on the priority for determining which of the paths to the same LU
is used as the switching destination, see
Paths on page
2-14
6-6.
2-19.
Figure 2-8 Path switching on page
2-15, the LU is accessed using only the path (A).
2-15.
HDLM Functions
Hitachi Dynamic Link Manager User Guide (for AIX(R))
offline (Places Paths Offline) on
Filtering of error information on page
2-15, the owner
Priority of Switching Destination
Path
2-31.
Figure 2-8