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Recovering the data
The sequential nature of tapes, combined with the unforgiving nature of many backup applications, means that it is often the case that a single data corruption, or a tape missing from a sequence of tapes, prevents access to a large volume of files.
If the backup catalogues for the data still exist then it is sometimes possible to perform a selective restore that avoids attempts to access the area where the problem was found, or any files from the tape that is missing. If not then it is almost certain that the only answer lies with a tape data recovery process.
At Altirium our tape recovery experts have been decoding data from backup tapes for over 20 years and we develop our own software for extracting the original files from within the encoded backup data. The software we develop allows us to overcome the logical corruption or missing data and restore the valid files that may be critical to you.
How tape data corruption can occur
Between reading the data from the disk to recording it on to the tape, the data being backed up can pass through a complex network of processes. Both logical processes such as backup agents, network buffering, re-blocking, checksum generation, compression and encryption and physical processes as data is transferred over networks and between devices, can all encounter errors.
Many applications attempt to detect these errors and report them at the time of the backup, however sometimes a problem can slip past. The only true methods for ensuring that the data that has been written correctly, and can be restored, is to verify the data immediately after the backup or perform a test restore from the tape. In our opinion restoration is the better option as this enables you to actually observe your files being restored and to check some of them. Due to the large volumes of data generally being backed up, the time involved to perform a data verification and the financial constraints within a business this is not always an option.
At the very least the backup logs should be checked, and any significant change to the time taken or the volume of data backed up should ring an alarm bell that something might be amiss. Be cautious though, this will tell you if something is definitely wrong but is not a true check that everything is right.
