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1.16.3. iSCSI Root
When accessing the root partition directly through a 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
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
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 Section 1.11, “Scanning iSCSI Interconnects”.
Configuring Timeouts for a Specific Session
You can also configure timeouts for a specific session and make them non-persistent (instead of using
/etc/iscsi/iscsid.conf
). To do so, run the following command (replace the variables accordingly):
iscsiadm -m node -T target_name -p target_IP:port -o update -n node.session.timeo.replacement_timeout -v $timeout_value
Important
The configuration described here is recommended for iSCSI sessions involving root partition access. For iSCSI sessions involving access to other types of storage (namely, in systems that use
dm-multipath
), refer to Section 1.16.2, “iSCSI Settings With dm-multipath
”.