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Dell EMC PowerVault MD 34XX/38XX Series Storage Arrays Administrator's Guide

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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, 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 virtual disk 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 an MD Series storage array, after a failed path is restored, failback does not occur automatically because the driver cannot autodetect 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 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 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.
  • If upgrading from a previous version of SLES, uninstall and then reinstall the latest scsi_dh_rdac module on the updated SLES installation. Then update the kernel and install the MD Storage Manager from the DVD.

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