Developers Guide

Server configuration
31 Dell EMC SC Series with Red Hat Enterprise Linux 7x | CML1071
To adjust the following timeout values, for a multipath enabled environment, open /etc/iscsi/iscsid.conf and
configure the following parameters:
 To control how often a NOP-Out request is sent to each target, configure the following parameter to 5
seconds instead of the default value of 10 seconds.
node.conn[0].timeo.noop_out_interval = 5
 To control the timeout value for the NOP-Out request, configure the following parameter to 5 seconds
instead of the default value of 15 seconds.
node.conn[0].timeo.noop_out_timeout = 5
 To control the timeout value for how long the iSCSI layer should wait before failing any commands to
queried paths, configure the following parameter to 5 seconds versus the default value of 15 seconds.
node.session.timeo.replacement_timeout = 5
The replacement_timeout command controls the wait time of a session re-establishment before failing the
pending SCSI commands. This includes commands that the SCSI layer error handler is passing up to a
higher level (such as multipath) or to an application if multipath is not active.
The NOP-Out section dictates that if a network problem is detected, the running commands are failed
immediately. The exception is if the SCSI layer error handler is running. To check if the SCSI error handler is
running, run the following command.
# iscsiadm -m session -P 3
Host Number: X State: Recovery
When the SCSI error handler is running, commands will not be failed until the seconds of the
node.session.timeo.replacement_timeout parameter are modified.
In multipath iSCSI environments where paths are managed by dm-multipath, configure iSCSI to monitor for
problems on the SAN (by sending out a NOP-Out request to each target) every 5 seconds. In addition, set
these requests to time out every 5 seconds. This manages and minimizes any latency in waiting for any single
path to recover by automatically resubmitting I/O requests to an alternate and still active iSCSI path.
The iSCSI configuration parameters NOP-Out and its associated time out value are managed by these two
entries in the /etc/iscsi/iscsid.conf file. Both entries default to 5 in RHEL 7.x.
node.conn[0].timeo.noop_out_interval = 5
node.conn[0].timeo.noop_out_timeout = 5
In multipath iSCSI use cases, this additional parameter in the /etc/iscsi/iscsd.conf file should be configured
from its default value of 120 to 5. This will dictate that the iSCSI layer should wait up to 5 seconds before
failing any commands to this path, thereby minimizing any latency and I/O wait.
node.conn[0].timeo.replacement_timeout = 5