Be careful using dd to write multiple volumes

[George Robbins]

In article <1990Oct10.051524.12610 at watcgl.waterloo.edu> idallen at watcgl.waterloo.edu (Ian! D. Allen [CGL]) writes:
> Ultrix 3.1C DS5400
> 
> I wrote some TK70 dump tapes like this:
>     dump 0f - /whatever | compress | dd ibs=8k obs=32k of=/dev/rmt0h
> Where the dd took two tapes, I cannot read it back:
>     dd bs=32k if=/dev/rmt0h | uncompress | restore if -
> 
> dd eventually asks for the next volume, then uncompress dies with some
> error about "not in compressed format" or some such when the second
> tape is started.  I havent got 600Mb of space to try extracting the
> two tapes into at the moment, to see if uncompress will read one 600Mb
> file off disk.  I imagine dd might be mis-handling the block that
> spans the two tapes.

Try specifying dd ibs=32k obs=1b on the restore.  This will be rather
slow, but may get you over the "discontinuity" during the reel switch.
I had similar problems with multi-file, multi-reel dumps.

-- 
George Robbins - now working for,     uucp:   {uunet|pyramid|rutgers}!cbmvax!grr
but no way officially representing:   domain: grr at cbmvax.commodore.com
Commodore, Engineering Department     phone:  215-431-9349 (only by moonlite)