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Do buffers mess with verification?   [Discuss]

By: Peter Shute       
Date: Jun 18,2018 at 20:20
In Response to: Do buffers mess with verification? (Ron Metzger)

> This problem reminds me of the Verify process on Tape Backup systems 30
> or so years ago. The Verify process use to write to tape, then shoeshine
> the tape back and re-read what it wrote, and compare against the source.
> It put so much wear and tear on the tape drive that the manufacturers
> eventually disallowed that form of verify. (Drives were failing so fast
> that something had to be done.) Instead they calculate (for x-amount of
> data) a CRC at the source, write the x-amount of data and store the CRC
> of that data on tape, later checking the Source CRC to the tape CRC. Even
> that was not very effective. Still produces a lot of shoe shining of the
> tape.

I remember having terrible trouble with tapes back then. Our first one had a second head that was supposed to allow verification by reading and writing nearly simultaneously. It would usually pass that verification, but a full verification after the backup often failed.

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