Compressing to a tape drive
ACPNET consultant
acp at ms.uky.edu
Fri Mar 9 04:59:45 AEST 1990
This is on an AT&T 6386 WGS running Sysv/386 3.2.1.
The hard disk in the machine is ~145 megabytes, and the tape drive only
holds 60meg, so I'm trying to fit a full disk backup on one tape with
something like
find . -print | cpio -oc | compress | dd [blocking options] > /dev/rmt/c0s0
Now, including dd in the pipe is *loads* faster than not including
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
no full input blocks, all partial blocks--I assume this corresponds to
bursts produced by compress. Something like bs=512 produces all full
blocks but doesn't affect the tape speed.
I assume something as slow as a tape drive could keep up with compress
if the buffering was done properly; it seems that when dd has a large
input buffer, it should hold off writing until the buffer was full;
this would at least allow the tape to stream for several records while
dd fills up its input buffer again.
Should I be using something other than dd? Any other suggestions?
Kenneth Herron
--
acp at ms.uky.edu University of Kentucky ACP Network Consultant
ukma!acp Dept. of Mathematics, room 715 POT (606) 257-2975
Lexington, KY 40506
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