HP Hitachi Dynamic Link Manager Software - Manual (Page 48)

2. HDLM Functions
26
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 in use will not be switched to the recovered owner path.
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 monitoring by the
dlnkmgr
command's
set
operation. For details on the
set
operation, see 6.6 set
(Sets Up the Operating Environment).
#
An intermittent error means an error that occurs irregularly because of, for
example, a loose cable connection.
2.8.2 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 6.5 online (Places Paths Online). For
details on the
offline
operation, see 6.4 offline (Places Paths Offline).
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 the Thunder 9500V Series, or Hitachi AMS/WMS series is being used, HDLM
selects the switching destination path from owner paths and then from 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 paths that access the same LU are candidates
for the switching destination path.
Paths are switched in units of physical paths. Therefore, if an error occurs in a path, all
the other paths that run through the same physical path are switched.