Iscsi Settings With Dm-Multipath - Red Hat ENTERPRISE LINUX - ONLINE STORAGE RECONFIGURATION GUIDE BETA Configuration Manual

Red Hat Enterprise Linux
Fibre Channel:
remove_on_dev_loss
If you prefer that devices are removed at the SCSI layer when links are marked bad (i.e. expired
after seconds), you can use the
dev_loss_tmo
remove_on_dev_loss
is in effect, the device will be added back once all transport problems are corrected.
Warning
The use of
the SCSI layer does not automatically unmount any file systems from that device.
When file systems from a removed device are left mounted, the device may not
be properly removed from multipath or RAID devices.
Further problems may arise from this if the upper layers are not hotplug-aware.
This is because the upper layers may still be holding references to the state of
the device before it was originally removed. This can cause unexpected behavior
when the device is added again.
7.2. iSCSI Settings With
If is implemented, it is advisable to set iSCSI timers to immediately defer
dm-multipath
commands to the multipath layer. To configure this, nest the following line under
/etc/multipath.conf
features
This ensures that I/O errors are retried and queued if all paths are failed in the
layer.
You may need to adjust iSCSI timers further to better monitor your SAN for problems. Available
iSCSI timers you can configure are NOP-Out Interval/Timeouts and
which are discussed in the following sections.
7.2.1. 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
them to the multipath layer. The multipath layer then retries those commands on another path. If
is not being used, those commands are retried five times before failing
dm-multipath
altogether.
10
.
. When a device is removed at the SCSI layer while
remove_on_dev_loss
dm-multipath
:
"1 queue_if_no_path"
is being used, the SCSI layer will fail those running commands and defer
module parameter
scsi_transport_fc
is not recommended, as removing a device at
replacement_timeout
remove_on_dev_loss
in
device {
dm-multipath
,