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Secondary backups from Veritas NetBackup, MP3 risk data loss

If you make secondary copies of your backups with Maintenance Pack 3 and either Veritas Software's NetBackup Server or NetBackup Enterprise Server 5.1, you run the risk of losing data, particularly if you use Virtual Tape Libraries.

Do you make secondary copies of your backups with either Veritas Software's NetBackup Server, a backup and recovery solution for midsized organizations, workgroups and remote offices, or with NetBackup Enterprise Server 5.1, which offers data protection that scales to protect the largest Windows environments, and with Maintenance Pack 3?

If so, you run the risk for data loss if you have multi-fragment non-multiplexed, duplicated images. According to Veritas, this can be a serious problem if the original backup copy is set to expire quickly and a restore has to be made from a copy of the copy.

This situation commonly occurs with Virtual Tape Libraries (VTLs), where the original copy is sent to the VTL and the information is quickly copied from the VTL's longer-term storage.

The problem exists if:

  • The original backup is written to tape or to a VTL.
  • The original backup spans more than one fragment -- for example, when a backup spans more than one tape or reaches the maximum fragment size.
  • The image is a duplicate and the source image was not multiplexed on tape.

If you make additional copies of the backup images using the "duplicate" operation in NetBackup, the images will be written incorrectly and any restores made from these copies will show some data loss. The affected files are the ones that cross fragment boundaries in the image.

Veritas officials point out that the problem does not affect disk-based backups at all or the original backup copy written to tape. If you have the original backup on tape, you can restore successfully from that.

The problem is specific to the bptm daemon in Maintenance Pack 3 and is fixed in Maintenance Pack 3a, which Veritas released last year.

Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in issues related to storage and storage management.

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