mkhaw@teknowledge-vaxc.UUCP (06/14/87)
I often use a pipe like
tar cBf - . | rsh remote dd of=/dev/rmt12 bs=20b
to make 9-track tapes from Unix hosts w/o local 9-track drives. If I then
try to read the tape on a host with a local 9-track drive using just tar alone,
I get a directory checksum error or a diagnostic about blocksize (I forget
which it is).
Should I omit "bs=20b", use another value for blocking, or is there an
additional parameter I can give to 'dd' in the above pipe -- like "conv=unblock"
-- so that I won't have to use a "dd | tar x" pipe to read back from the tape?
By the way, when tar'ing (1) to 6250bpi 9-track, (2) over ethernet, are
there larger blocksizes I can use? The Ultrix man file for tar claims
the default 20 blocks (of 512 bytes) is the maximum for 9 track tape, but
I've used 126b with no problem, like a lot of Sun s/w vendors do for 1/4 in.
tar cartridges.
Thanks,
Mike Khaw
--
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USnail: Teknowledge Inc, 1850 Embarcadero Rd, POB 10119, Palo Alto, CA 94303moore@ucbcad.UUCP (06/14/87)
Instead of tar cBf - . | rsh remote dd of=/dev/rmt12 bs=20b use tar cBf - . | rsh remote dd of=/dev/rmt12 obs=20b setting bs causes no reblocking to be done, the blocks written are the same size as the blocks read. Unfortunately, your ethernet is fracturing your blocks, so your tape is getting fractured blocks as well. Setting obs=20b guarantees the tape blocks are all precisely 20b long. You might want to set ibs=20b as well, the default is 1b and probably (maybe?) inefficient. Peter Moore moore@ic.Berkeley.edu ...!ucbvax!moore