[lug] hard drive failure

[Sean Reifschneider]

On 10/02/2009 10:29 AM, Matt James wrote:
> Last couple of people I have recommended this type of solution to have
> not done it because of the shear cost involved.  You have to come to

Yeah, data recovery places are great: They know that when you call them
they have you by the danglies, and they aren't afraid to charge for it.
;-/

We've only dealt with a data recovery place once, and that was for a DDS
tape recovery.  The backup software had been doing a full backup and then
overwriting the incremental backups at the end of the tape.  There's no way
with commercial hardware (without very special debugging firmware) to skip
past an EOD mark on DDS.

I even had tried (on a test tape) the "start writing data, enough
to blow past the EOD mark, then unplug the drive" trick.  The EOD is
written to the BEGINNING of the tape in DDS, in a kind of super-block
("Hi, the data ends X blocks down the tape").

I don't honestly remember who was used for this, but I wasn't particularly
impressed with them.  I had written a letter explaining that the data on
the tape was compressed on a file-by-file basis, and we just wanted them to
stream all the data off the tape and we'd take it from there.

They looked at it and then shipped the tape back via ground shipping,
despite our client paying for expedited recovery service.  They didn't
actually recover anything because "The data is compressed, and losing the
beginning of the data makes it unrecoverable."  So we had to wait a week
for the ground shipping to show up, fedex it back to them, and have them
stream the data off and send it back to us.

The format was kind of like a tar file where each file is compressed
individually.  Once I had the data stream, I was able to recover the data
by searching through it looking for the first file marker record that I
could find, and then just using that to extract the files beyond that.

They were right, had the tape been compressed by something like "tar cf / |
bzip2 >/dev/rst0", we would have been hosed.  So remember kids: For maximum
recoverability compress the files individually and then archive them.  This
applies just as well to CDs or DVDs as it does to tape.

Sean
-- 
Sean Reifschneider, Member of Technical Staff <jafo at tummy.com>
tummy.com, ltd. - Linux Consulting since 1995: Ask me about High Availability

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