Path: utzoo!attcan!uunet!husc6!think!samsung!cs.utexas.edu!ssbn!bill
From: bill@ssbn.WLK.COM (Bill Kennedy)
Newsgroups: comp.unix.i386
Subject: Re: Tape backup performance on 386 ISA/EISA systems
Summary: pax does well too
Keywords: tape, performance, 386
Message-ID: <1512@ssbn.WLK.COM>
Date: 10 Jun 90 15:05:33 GMT
References: <1060@sixhub.UUCP> <770@mwtech.UUCP> <1123@sixhub.UUCP> <1990Jun10.114934.17744@virtech.uucp>
Reply-To: bill@ssbn.WLK.COM (Bill Kennedy)
Distribution: na
Organization: W.L. Kennedy Jr. and Associates, Pipe Creek, TX
Lines: 37

In article <1990Jun10.114934.17744@virtech.uucp> cpcahil@virtech.UUCP (Conor P. Cahill) writes:
>In article <1123@sixhub.UUCP> davidsen@sixhub.UUCP (bill davidsen) writes:
>>  [ slow tape performance ... ]
>
>The only reason I could see for this kind of difference is that you are
>using backup software that does not have a large tape buffer (i.e. tar).
>
>Using a tape backup archiver with large buffers (like cpio -C 102400)
>will negate most of the effect of a fragmented disk on tape streaming.
>-- 
>Conor P. Cahill            (703)430-9247        Virtual Technologies, Inc.,
>uunet!virtech!cpcahil                           46030 Manekin Plaza, Suite 160

Agreed, and a small addition.  One of my neighbors uses gnu tar and gets
very good performance out of his tape.  I had used cpio with the -C option
and I got decent performance but I would get five to nine stops per cpio
block.  Bill figures, as he points out, and just not acceptable.  I ran into
another problem with cpio that caused me to switch to pax.

I originally thought the problem was with the CompuAdd hard cache controller
but it appeared again with a WD1007-SE2.  When I switched to the second
tape cartridge the residue from the first would write out OK but the system
would just freeze as it was getting ready to write the first block of the
second volume.  I decided to try pax and I got two bonuses.

The first bonus was obvious, the system doesn't freeze (by "freeze" I mean
that it's off in a loop somewhere, reset and only reset/power cycle to
recover).  The second is that a block is written with one movement of the
tape.  The speed improvement isn't dramatic but it's noticable.  Pax is
also a little more flexible about defining block sizes.  With cpio you have
to specify in bytes and ASSume the trailing zero.  Pax lets you specify in
bytes, blocks, Kbytes, or Mbytes.  I mention this because if you specify the
block size too large you'll end up paging to swap space and that's a double
disk I/O penalty.
-- 
Bill Kennedy  usenet      {texbell,att,cs.utexas.edu,sun!daver}!ssbn!bill
              internet    bill@ssbn.WLK.COM   or attmail!ssbn!bill