Limitations And Known Issues - Dell PowerVault MD3220 Owner's Manual

Limitations and Known Issues

• In certain error conditions with the no_path_retry or the
queue_if_no_path feature is set, applications may hang. To overcome
these conditions the you must enter the following command for each
affected multipath device:
dmsetup message [device] 0 "fail_if_no_path"
where [device] is the multipath device name (for example. mpath2; do
not specify the path)
• 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 MD3200 Series array, after a failed path is restored, failback does
not automatically occur 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 also
experiences 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.
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Configuration: Device Mapper Multipath for Linux