39.3. iSCSI Root

When accessing the root partition directly through an iSCSI disk, the iSCSI timers should be set so that iSCSI layer has several chances to try to reestablish a path/session. In addition, commands should not be quickly re-queued to the SCSI layer. This is the opposite of what should be done when dm-multipath is implemented.

To start with, NOP-Outs should be disabled. You can do this by setting both NOP-Out interval and timeout to zero. To set this, open /etc/iscsi/iscsid.conf and edit as follows:

node.conn[0].timeo.noop_out_interval = 0
node.conn[0].timeo.noop_out_timeout = 0

node.conn[0].timeo.noop_out_interval = 0
node.conn[0].timeo.noop_out_timeout = 0

In line with this, replacement_timeout should be set to a high number. This will instruct the system to wait a long time for a path/session to reestablish itself. To adjust replacement_timeout, open /etc/iscsi/iscsid.conf and edit the following line:

node.session.timeo.replacement_timeout = replacement_timeout

node.session.timeo.replacement_timeout = replacement_timeout

After configuring /etc/iscsi/iscsid.conf, you must perform a re-discovery of the affected storage. This will allow the system to load and use any new values in /etc/iscsi/iscsid.conf. For more information on how to discover iSCSI devices, refer to Chapter 36, Scanning iSCSI Targets with Multiple LUNs or Portals.

iscsiadm -m node -T target_name -p target_IP:port -o update -n node.session.timeo.replacement_timeout -v $timeout_value

# iscsiadm -m node -T target_name -p target_IP:port -o update -n node.session.timeo.replacement_timeout -v $timeout_value