Dell MD3200, MD3220 owner manual Limitations and Known Issues, 174

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

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Configuration: Device Mapper Multipath for Linux