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The Backup Task Fails when the Storage Device Recovers from a Power Failure in Deduplication

Publication Date:  2015-07-31 Views:  66 Downloads:  0
Issue Description
Product and version: VTL6000 V100R003

If the storage device loses power when the VTL server is performing deduplication, the ongoing deduplication operation stops. After the storage device regains power and starts a backup task, one tape cannot be loaded by the drive, and two tapes are found present in the same slot in the navigation tree of the VTL Console.

The symptoms are:

1.  In the navigation tree of the VTL Console, choose Virtual Tape Library System > Deduplication Policies and select a deduplication policy. Then click Event Log in the function pane, and error information is found.

2.  In the navigation tree of the NetBackup Administration Console, select Activity Monitor. The backup task is in the Waiting state.

3.  In the navigation tree of the VTL Console, choose Virtual Tape Library System > Virtual Tape Library. No tape is loaded on the drive.

4.  In the navigation tree of the VTL Console, choose Virtual Tape Library System > Virtual Tape Library > Tapes. Two tapes have the same slot ID. Click the General tab in the function pane to view the allocation type of the tapes.
  • If the tapes' allocation type is virtual tape, the data on the tape is the original data.
  • If the tapes' allocation type is virtual tape (mixed VIT), the data on the tape contains the original data and the original virtual index.
  • If the tapes' allocation type is virtual tape (pure VIT), the data on the tape is the virtual index.
Handling Process
1.  In the navigation tree of the VTL Console, choose Virtual Tape Library System > Virtual Tape Library > Tapes to view the medium types of tapes.

2.  Delete the tapes whose medium type is SIRXXX, where XXX is the virtual tape number. This type of tapes refers to the tapes that were generated by the SIR server during deduplication.

3.  Right-click VTL Server > Option > Deduplication > Reclamation > Start Space Reclamation to reclaim the data stored in the SIR data storage space before the deduplication process is interrupted.
Root Cause
If the ID of the tape that is being deduplicated is 28 and the tape 28 stores the original data, the deduplication process is as follows:

1.  The VTL server generates a tape for storing indexes. Assume the ID of this tape is 29.

2.  The SIR server loads tape 28 and tape 29, and then scans for tape 28.

3.  When scanning for tape 28, the SIR server stores the indexes generated by deduplication to tape 29, and stores the data blocks generated by deduplication to the SIR data storage space.

4.  When the scan is complete, the SIR server converts tape 29's allocation type to virtual index tape (VIT).

5.  The VTL server exchanges the IDs of tape 28 and tape 29. After the exchange is complete, tape 28's allocation type becomes VIT and store the indexes, whereas tape 29 stores the original data.

6.  Tape 29 is moved to the virtual vault.

7.  Tape 29 is deleted. The deduplication process is complete.

If the storage device loses power when the VTL server is performing deduplication, the ongoing deduplication operation stops. However, the tape that is being deduplicated is not deleted and the new tape used to store virtual indexes is also not deleted. If the tape that is being deduplicated resides in the same slot as the VIT, the backup task may fail: when the robot arm fetches the tape of this slot to store backup data, the drive cannot determine which tape to load.

The possible cause of this problem is that the storage device loses power when the SIR server is scanning for tape 28 or exchanging IDs of tape 28 and tape 29.

END