Compressing to a tape drive

[John Plocher]

+-- In <14496 at s.ms.uky.edu> acp at ms.uky.edu (ACPNET consultant) writes
| This is on an AT&T 6386 WGS running Sysv/386 3.2.1.
| 
| find . -print | cpio -oc | compress | dd [blocking options] > /dev/rmt/c0s0
| it, but I haven't been able to find any dd options which let the 
| tape stream.  It keeps stopping and backing up.  When using something
| like ibs=32k obs=512 (the tape writes 512-byte records), dd reports
+--

Try something like

    find . -print | cpio -oc | compress | dd of=/dev/rmt/c0s0 -obs 1024k

this writes 1Mb at a time to the tape - and the drive *will*
stream.  Don't worry about tape blocking - the QIC tapes are
set up to do all blocking internally, unlike the 9 track reel
tape drives you may be familiar with...

You may also want to explore the different cpio options avaliable:
	-I rawdevice which selects the Input device,
	-O rawdevice which selects the Output device, and
	-C size      which specifies a blocking size

-I and -O will detect end of tape and prompt you to change tapes
and press return when ready to continue ...

    find . -print | cpio -oc -O /dev/rst/c0s0 -C 102400

Lastly, there are several programs on the net that are replacements
for either cpio (afio), or dd (ddd) which allow double buffering,
multi-process buffering, ... which may be another solution to your
problems...

  -John