Dell MD3620I, MD3600I owner manual Troubleshooting, 194, Question Answer

•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 CPU 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 CPU 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 –lllists vendor/product ID, which can help identify this issue.

Troubleshooting

Question Answer

How can I check if multipathd is running?

Why does the multipath –ll command output not show any devices?

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 been updated with proper settings. After this, run multipath. Then run multipath –ll, the new devices should show up.

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.

Run rescan_dm_devs in any directory. This should bring up the devices.

Run rescan_dm_devs instead of rescan- scsi-bus for LUN 0 reconfiguration.

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Configuration: Device Mapper Multipath for Linux