Troubleshooting - Dell POWERVAULT MD3620I Owner's Manual

• 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
How can I check if multipathd is
running?
Why does the multipath –ll
command output not show any
devices?
Why is a newly-mapped LUN not
assigned a multipathing device
node?
I have no LUNs mapped before.
Then I map some LUNs. After
running rescan-scsi-bus.sh, LUN 0
doesn't show up.
Answer
Run the following command.
/etc/init.d/multipathd status
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.
Run rescan_dm_devs in any directory. This
must bring up the devices.
Run rescan_dm_devs instead of rescan-
scsi-bus for LUN 0 reconfiguration.
Configuration: Device Mapper Multipath for Linux
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