Corrupted tape backup. 4189

Hi all,

Tape backup systems are quite reliable but can be tricky. I work for a software engineering company that specializes in backup & disaster recovery of large information systems. We support government agencies, universities, and high performance computing centers. As such, I see failures of all sorts. Some suggestions to the users of tape backup systems . . . Mirroring tapes is very prudent. The verification step is important but can not butture you that you won't experience degradation of the media over time. Also, flaky drives have been known to damage media and that may be hard to immediately detect-confirm.

Some software packages will be able to work around bad spots on the media and give you an accurate buttessment of what files have not been restored. Depending upon the package you may be able to recover those files from previous incrementals on other tapes. My firm has developed a technology that will take just the daily or differential changes from a client system after the initial full backup. It reuses data already in the backup system to produce lower level backups (i.e. weekly's monthly's semi-annual, and even full backups entirely on the server. The advantage to this approach is that a failed tape can generally be reconstructed with other data in the system.

Keeping tapes for a set period of time (you can set your own tape retension policies and rotate them back into service at a given point) is also very useful for point in time restores. Periodic full backups have historically been used to shorten restore times and reduce the number of tape reads. However, if you experience a bit flip in a given data set and it goes undetected, then your new full backup will checksum the corrupted file and buttume that all is well. When you recycle your other tapes you will be essentially throwing out your valid copy of that file in favor of the corrupted new matrix. A point in time restore could actually prove more useful than a current corrupted file.

Mirror some of your tapes, retain some of the mirrors for extended periods, and consider synthetic backup consolidation technology to maintain and reuse original file images. Please feel free to visit our site or contact me with questions. My time monitoring this bbs is limited and infrequent but I am happy to help.