HP XP Racks - Manual (Page 46)

The last available online path for each LU cannot be placed offline by
executing the offline operation. This ensures access to the LU. For details
on the offline operation, see offline (Places Paths Offline) on page 6-6 .
If an error occurs in the last available online path for each LU, the status of
the path is changed to Online(E).
If you are using automatic failback, when the path recovers from an error,
HDLM automatically places the path online.
When you are using intermittent error monitoring, the path in which the
intermittent error occurred is not automatically placed online when the path
recovers from the error. In such a case, place the path online manually.
Note
If there is a path failure immediately after a path is taken offline by using
either the an HDLM command, the status might change from Offline(C)
to Offline(E). If an offline operation was just performed, wait about 2
minutes, check the path status by using an HDLM command, and then
make sure that the status has changed to Offline(C). If it is still
Offline(E), retry the offline operation.
Monitoring intermittent errors (functionality when
automatic failback is used)
An intermittent error refers to an error that occurs irregularly because of
something like a loose cable. In such a case, I/O performance might decrease
while an automatic failback is being performed to repair an intermittent error.
This is because the automatic failback operation is being performed
repeatedly (because the intermittent error keeps occurring). To prevent this
from happening, HDLM can automatically remove the path where an
intermittent error is occurring from the paths that are subject to automatic
failbacks. This process is called intermittent error monitoring.
We recommend that you use intermittent error monitoring along with the
automatic failback function.
A path in which an error occurs a specified number of times within a specified
interval is determined to have an intermittent error. The path where an
intermittent error occurs has an error status until the user chooses to place
the path back online. Failbacks are not performed for such paths. This status
is referred to as the not subject to auto failback status.
Checking intermittent errors
You can check the paths in which intermittent errors have occurred by
viewing the execution results of the HDLM command's view operation.
For details on the view operation, see view (Displays Information) on page
6-34 .
2-24
HDLM Functions
Hitachi Dynamic Link Manager (for AIX) User Guide