Networker

Re: [Networker] Auto media verify?

2004-05-07 11:13:48
Subject: Re: [Networker] Auto media verify?
From: Steve Rader <rader AT GINSENG.HEP.WISC DOT EDU>
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Date: Fri, 7 May 2004 10:13:40 -0500
 > > DLT (and most all modern tape technologies, IIRC) do "read after
 > > write", so DLT drives automatically verify that all the data they
 > > receive is written to tape.  That leads me to think that auto media
 > > verify is not necessary, at least when writing to DLT.
 > >
 > > So I'm still left wondering: is there some compelling reason
 > > to set auto media verify?  (If the answer is yes, I would think
 > > Legato would make it a default setting or at least mention it in
 > > doc/release notes.)

 > The question is, does DLT (or other technology) acknowledge the write
 > before or after verifying the tape.  If it's before the verification,
 > then a situation could arise where the verification fails and there is
 > not enough tape left in the cartridge to rewrite the buffer.  I'll bet
 > that is the case.

...doesn't this hypothesis imply that DLT drives are quite broken
by design???


 > My understanding is that DLT has a "warning" mark some distance from the
 > end (EOT vs EOM).  The drive should attempt to write all buffered data
 > after reaching the warning mark and then return EOT to the host.  If
 > true, then this particular issue is probably not a big deal for DLT
 > users.  I have no idea if other technology deals with it in similar ways
 > or not.

...tf this understanding is true, then wouldn't the above
hypothesis would be false??


Apologies for being especially ornery today.

Has anyone read the last saves on some DLT tapes lately?
=:)

Perhaps it's worth pointing out that if we second-guess
vendor's specs, software's functionality, and the like, then
there would be no time to get any real work done!

steve
- - -
systems & network guy
high energy physics
university of wisconsin

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