Hello David

I used to come across variable block size problems all the time with various
Seismic formats, what I found was that if you simply dd with a block size larger
than the largest that you'd expect to encounter on the tape, dd will produce a
faithful copy but will complain about copying over nothing but partial blocks.
So long as you're not pedantic about the block count message that dd will print
on the screen, it will work and be relatively painless.

Yes, I too went through a period of time when I kept doing mt bsf to back over a
end of file marker so that I could do each record with an appropriately
formulated dd command but then one day I said "What the hell..." and typed in a
huge block factor and was pleasantly surprised.

Regards,
John I Wang
Sr. Systems Engineer
Steverson Information Professionals

---
Enron Broadband Services
3 Allen Center, Room 337C
PH (713) 345-6238




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  |       To:     david AT datastaff DOT com                                    
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  |       cc:     Devon_Buffington AT aimfunds DOT com,                         
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  |       veritas-bu AT mailman.eng.auburn DOT edu, (bcc: John 
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  |       Communications)                                                      |
  |       Subject:     Re: [Veritas-bu] Duplicating tapes                      |
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The problem with dd'ing Netbackup tapes is the block factor.  You have to
use the corrct block factor when you dd to make an useable tape.  For
non-NDMP tapes, it's fairly simple 'cause the first tape file is 2 blocks
(1k) which is the tape lable, and the remaining tape files are all with
block factor of 64 (32k block) if your backup server is on Solaris.

For NDMP tapes however, the NDMP tape file has variable record size.
I remember the first *record* of a NDMP backup image (tape file) is 2k (I
could be a bit off here), and the remaining of the NDMP backup image has the
block factor of 126 (63k record size).  Getting this right while dd'ing
isn't that straigtforward.

dd'ing Netbackup tape isn't as easy as it seems.

...