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Dell PowerVault ME4 Series Storage System Administrator’s Guide

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Removing a disk group from quarantine

Contact technical support for assistance in determining if the recovery procedure that makes use of the Dequarantine Disk Group panel and the trust command is applicable to your situation and for assistance in performing it.

CAUTION:Carefully read this topic to determine whether to use the Dequarantine Disk Group panel to manually remove a disk group from quarantine.
NOTE:For status descriptions, see Related Disk Groups table.
  • The Dequarantine Disk Group panel should only be used as part of the emergency procedure to attempt to recover data and is normally followed by use of the CLI trust command. If a disk group is manually dequarantined and does not have enough disks to continue operation, its status will change to offline (OFFL) and its data may or may not be recoverable through use of the trust command.
  • See the help for the trust command.
  • To continue operation—that is, not go to quarantined status—a RAID-3 or RAID-5 disk group can have only one inaccessible disk; a RAID-6 disk group can have only one or two inaccessible disks; a RAID-10 or RAID-50 disk group can have only one inaccessible disk per sub-disk group. For example, a 16-disk RAID-10 disk group can remain online (critical) with 8 inaccessible disks if one disk per mirror is inaccessible.
  • The system will automatically quarantine a disk group having a fault-tolerant RAID level if one or more of its disks becomes inaccessible, or to prevent invalid, or stale data that may exist in the controller from being written to the disk group. Quarantine will not occur if a known-failed disk becomes inaccessible or if a disk becomes inaccessible after failover or recovery. The system will automatically quarantine an NRAID or RAID-0 disk group to prevent invalid data from being written to the disk group. If quarantine occurs because of an inaccessible disk, event 172 is logged. If quarantine occurs to prevent writing invalid data, event 485 is logged.
Examples of when quarantine can occur are:
  • At system power-up, a disk group has fewer disks online than at the previous power-up. This may happen because a disk is slow to spin up or because an enclosure is not powered up. The disk group will be automatically dequarantined if the inaccessible disks come online and the disk group status becomes FTOL, or if after 60 seconds the disk group status is QTCR or QTDN.
  • During system operation, a disk group loses redundancy plus one more disk. For example, three disks are inaccessible in a RAID-6 disk group or two disks are inaccessible for other fault-tolerant RAID levels. The disk group will be automatically dequarantined if after 60 seconds the disk group status is FTOL, FTDN, or CRIT.
Quarantine isolates the disk group from host access and prevents the system from changing the disk group status to OFFL. The number of inaccessible disks determines the quarantine status, from least to most severe:
  • QTDN (quarantined with a down disk): The RAID-6 disk group has one inaccessible disk. The disk group is fault tolerant but degraded. If the inaccessible disks come online or if after 60 seconds from being quarantined the disk group is QTCR or QTDN, the disk group is automatically dequarantined.
  • QTCR (quarantined critical): The disk group is critical with at least one inaccessible disk. For example, two disks are inaccessible in a RAID-6 disk group or one disk is inaccessible for other fault-tolerant RAID levels. If the inaccessible disks come online or if after 60 seconds from being quarantined the disk group is QTCR or QTDN, the disk group is automatically dequarantined.
  • QTOF (quarantined offline): The disk group is offline with multiple inaccessible disks causing user data to be incomplete, or is an NRAID or RAID-0 disk group.

When a disk group is quarantined, its disks become write-locked, its volumes become inaccessible, and it is not available to hosts until it is dequarantined. If there are interdependencies between the quarantined disk group's volumes and volumes in other disk groups, quarantine may temporarily impact operation of those other volumes. Depending on the operation, the length of the outage, and the settings associated with the operation, the operation may automatically resume when the disk group is dequarantined or may require manual intervention. A disk group can remain quarantined indefinitely without risk of data loss.

A disk group is dequarantined when it is brought back online, which can occur in three ways:
  • If the inaccessible disks come online, making the disk group FTOL, the disk group is automatically dequarantined.
  • If after 60 seconds from being quarantined the disk group is QTCR or QTDN, the disk group is automatically dequarantined. The inaccessible disks are marked as failed and the disk group status changes to critical (CRIT) or fault tolerant with a down disk (FTDN). If the inaccessible disks later come online, they are marked as leftover (LEFTOVR).
  • The dequarantine command is used to manually remove a disk group from quarantine. If the inaccessible disks later come online, they are marked as leftover (LEFTOVR). If event 485 was logged, use the dequarantine command only as specified by the recommended-action text to help prevent data corruption or loss.

A quarantined disk group can be fully recovered if the inaccessible disks are restored. Make sure that all disks are properly seated, that no disks have been inadvertently removed, and that no cables have been unplugged. Sometimes not all disks in the disk group power up. Check that all enclosures have restarted after a power failure. If these problems are found and then fixed, the disk group recovers and no data is lost.

If the inaccessible disks cannot be restored (for example, they failed), and the disk group's status is FTDN or CRIT, and compatible spares are available, reconstruction will automatically begin.

If a replacement disk (reconstruct target) is inaccessible at power up, the disk group becomes quarantined. When the disk is found, the disk group is dequarantined and reconstruction starts. If reconstruction was in process, it continues where it left off.

NOTE:The only tasks allowed for a quarantined disk group are Dequarantine Disk Group and Remove Disk Groups. If you delete a quarantined disk group and its inaccessible disks later come online, the disk group will reappear as quarantined or offline and you must delete it again to clear those disks.

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