Dell PowerVault MD3200i Manuel d'utilisateur Page 200

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198 Configuration: Device Mapper Multipath for Linux
After a failed path is restored on an MD3600i Series array, failback does not
occur automatically because the driver cannot auto-detect devices without
a forced rescan. Run the command
rescan_dm_devs
to force a rescan
of the host server. This restores the failed paths enabling failback to occur.
Failback can be slow when the host system is experiencing heavy I/O. The
problem is exacerbated if the host server is also experiencing very high
processor utilization.
The Device Mapper Multipath service can be slow when the host system is
experiencing heavy I/O. The problem is exacerbated if the host server is
also experiencing very high processor utilization.
If the root disk is not blacklisted in the multipath.conf file, a multipathing
node may be created for the root disk. The command
multipath –ll
lists vendor/product ID which can help identify this issue.
Troubleshooting
Question Answer
How can I check if multipathd is
running?
Run the following command.
/etc/init.d/multipathd status
Why does the multipath –ll
command output not show any
devices?
First verify if the devices are discovered or not.
The command #cat /proc/scsi/scsi
displays all the devices that are already
discovered. Then verify the multipath.conf to
ensure that it is updated with proper settings.
After this, run multipath. Then run
multipath –ll, the new devices must show
up.
Why is a newly-mapped LUN not
assigned a multipathing device
node?
Run rescan_dm_devs in any directory. This
must bring up the devices.
I have no LUNs mapped before.
Then I map some LUNs. After
running rescan-scsi-bus.sh, LUN 0
doesn’t show up.
Run rescan_dm_devs instead of rescan-
scsi-bus for LUN 0 reconfiguration.
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