Installation guide

Chapter 21. Online Storage Management
144
21.16.2.1. NOP-Out Interval/Timeout
To help monitor problems the SAN, the iSCSI layer sends a NOP-Out request to each target. If a NOP-
Out request times out, the iSCSI layer responds by failing any running commands and instructing the
SCSI layer to requeue those commands when possible.
When dm-multipath is being used, the SCSI layer will fail those running commands and defer
them to the multipath layer. The multipath layer then retries those commands on another path. If dm-
multipath is not being used, those commands are retried five times before failing altogether.
Intervals between NOP-Out requests are 10 seconds by default. To adjust this, open /etc/iscsi/
iscsid.conf and edit the following line:
node.conn[0].timeo.noop_out_interval = [interval value]
Once set, the iSCSI layer will send a NOP-Out request to each target every [interval value]
seconds.
By default, NOP-Out requests time out in 10 seconds
9
. To adjust this, open /etc/iscsi/
iscsid.conf and edit the following line:
node.conn[0].timeo.noop_out_timeout = [timeout value]
This sets the iSCSI layer to timeout a NOP-Out request after [timeout value] seconds.
SCSI Error Handler
If the SCSI Error Handler is running, running commands on a path will not be failed immediately
when a NOP-Out request times out on that path. Instead, those commands will be failed after
replacement_timeout seconds. For more information about replacement_timeout, refer to
Section 21.16.2.2, “replacement_timeout”.
To verify if the SCSI Error Handler is running, run:
iscsiadm -m session -P 3
21.16.2.2. replacement_timeout
replacement_timeout controls how long the iSCSI layer should wait for a timed-out path/session
to reestablish itself before failing any commands on it. The default replacement_timeout value is
120 seconds.
To adjust replacement_timeout, open /etc/iscsi/iscsid.conf and edit the following line:
node.session.timeo.replacement_timeout = [replacement_timeout]
The 1 queue_if_no_path option in /etc/multipath.conf sets iSCSI timers to immediately
defer commands to the multipath layer (refer to Section 21.16.2, “iSCSI Settings With dm-
multipath”). This setting prevents I/O errors from propagating to the application; because of this,
you can set replacement_timeout to 15-20 seconds.
9
Prior to Red Hat Enterprise Linux 5.4, the default NOP-Out requests time out was 15 seconds.