Veritas-bu

Re: [Veritas-bu] Tapeless backup environments

2007-10-25 16:18:23
Subject: Re: [Veritas-bu] Tapeless backup environments
From: A Darren Dunham <ddunham AT taos DOT com>
To: veritas-bu AT mailman.eng.auburn DOT edu
Date: Thu, 25 Oct 2007 20:01:35 +0000
> Did I read in this list that netbackup was supposed to do some kind of
> checksum on the data written to tape?
> If so would a bpverify check this. I would assume that if netbackup does
> this it would find the error.
> because netbackup would do it's calc before passing the block to the
> dedupe hardware/software. And the block that it gets back from the
> dedupe hardware/software would be different.

Even if bpverify did checksum in this manner, you can't assume that it
would find all such errors.  The checksum can collide in a manner
identical to the hash.  Unless it lined up exactly with the hash
algorithm, it would likely provide some additional protection, but at
the same time it must include some collisions where both the block hash
and the overall checksum give identical values for a replacement block.
The presense of an additional checksum like this changes the specific
numbers, but does not change the essential character of the issue.

-- 
Darren Dunham                                           ddunham AT taos DOT com
Senior Technical Consultant         TAOS            http://www.taos.com/
Got some Dr Pepper?                           San Francisco, CA bay area
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