System information

Important
Whether your considerations are failover speed or security, the recommended value for
repl acement_ti meo ut will depend on other factors. These factors include the network,
target, and system workload. As such, it is recommended that you thoroughly test any new
configurations to repl acements_ti meo ut before applying it to a mission-critical system.
25.16.3. 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
d m-mul ti path 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/i scsi /i scsi d. co nf and edit as follows:
node.conn[0].timeo.noop_out_interval = 0
node.conn[0].timeo.noop_out_timeout = 0
In line with this, repl acement_ti meo ut 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 repl acement_ti meo ut,
open /etc/i scsi /i scsi d . co nf and edit the following line:
node.session.timeo.replacement_timeout = replacement_timeout
After configuring /etc/i scsi /i scsi d. co nf, you must perform a re-discovery of the affected
storage. This will allow the system to load and use any new values in /etc/i scsi /i scsi d. co nf.
For more information on how to discover iSCSI devices, refer to Section 25.12, “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/i scsi /i scsi d. co nf). 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 d m-mul ti path), refer to Section 25.16.2, “iSCSI Settings With d m-mul ti path” .
25.17. Cont rolling t he SCSI Command T imer and Device St at us
Configuring T imeout s for a Specific Session
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