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Knowledge Base

Unexpected Storage Device Power-Off During a Deduplication Leads to a Backup Failure After the Device Is Powered On

Publication Date:  2013-05-06  |   Views:  186  |   Downloads:  0  |   Author:  c90002397  |   Document ID:  EKB1000027547

Contents

Issue Description

The deduplication on the VTL server stops due to an unexpected storage device power-off. When a backup task is performed after the storage device is powered on again, a tape fails to be loaded on the drive. As shown in the VTL Console navigation tree, two tapes are in the same slot.
The symptoms are:
1. In the VTL Console navigation tree, choose Virtual Tape Library System > Deduplication Policies, and select a deduplication policy. Then click Event Log in the function pane to view fault information.
2. In the NetBackup Console navigation tree, select Activity Monitor. The backup task is in the Waiting state.
3. In the VTL Console navigation tree, choose Virtual Tape Library System > Virtual Tape Library. No tape is loaded on the drive.
4. In the VTL Console navigation tree, choose Virtual Tape Library System > Virtual Tape Library > Tapes. Two tapes have the same slot number. Click General in the function pane to view the allocation types of the tapes.
− If the tape's allocation type is virtual tape, the data on the tape is the original data.
− If the tape's allocation type is virtual tape (mixed VIT), the data on the tape contains the original data and the previous virtual index.
− If the tape's allocation type is virtual tape (pure VIT), the data on the tape is virtual index.

Alarm Information

None.

Handling Process

Step 1 In the VTL Console navigation tree, choose Virtual Tape Library System > Virtual Tape Library > Tapes to view the tape medium types.
Step 2 Delete the tapes with medium types SIRXXX, where XXX is the tape number, because these tapes are newly created by the SIR server during the deduplication.
Step 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 is interrupted.

Root Cause

Assuming that the virtual ID of the tape on which the deduplication is performed is 28, the following describes the deduplication process:
1. The VTL server creates a new tape for storing the index. It is assumed that the virtual ID of this newly created disk is 29.
2. The SIR server loads tape 28 and tape 29, and scans tape 28.
3. When scanning tape 28, the SIR server stores the index generated by the deduplication to tape 29, and stores the deduplicated data blocks to the SIR data storage space.
4. When the scan has completed, the SIR server converts tape 29's allocation type to VIT.
5. The VTL server exchanges the virtual IDs of tape 28 and tape 29. After the exchange, tape 28's allocation type becomes VIT, that is, tape 28 is storing the index, and tape 29 is for storing the original data.
6. Tape 29 is moved to the virtual vault.
7. Tape 29 is deleted. The deduplication process is complete.
A storage device power-off during a deduplication process may lead to a deduplication failure. The tape on which the deduplication is performed has not been deleted. Neither has the newly created tape for storing the index. If the tape on which the deduplication is performed and the tape for storing the virtual index are in the same slot, backup tasks may fail. Because if the disk arm attempts to store backup data to the tape in this slot, the drive fails to determine which tape is to be loaded.
Possible cause is the storage device powers off when the SIR server is scanning tape 28 or when the virtual IDs of tape 28 and tape 29 are being exchanged.

Suggestions

None.