Configuration: Device Mapper Multipath for Linux 185
• I/O may hang when a Device Mapper device is deleted before the volume
is unmounted.
• If the scsi_dh_rdac module is not included in initrd, slower device
discovery may be seen and the syslog may become populated with buffer
I/O error messages.
• I/O may hang if the host server or storage array is rebooted while I/O is
active. All I/O to the storage array should be stopped before shutting down
or rebooting the host server or storage array.
• With the MD3200i Series array, after a failed path is restored, 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
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 –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
book.book Page 185 Wednesday, May 26, 2010 2:14 PM