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Date:	Wed, 31 Jul 2002 22:10:33 PST7
From:	Peter Skye <pskye@peterskye.com >
Reply-To:	scoug-help@scoug.com
To:	scoug-help@scoug.com
Subject:	SCOUG-Help: Re: Drive Image Backups

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> > Compression speeds things up (there's less I/O)
>
> Compression should do exactly the opposite of what you stated.

With compression you spend *more* time in cpu processing (doing the
actual compression) but you write *fewer* bytes to the hard drive.

With a fast processor and a slow drive, you're I/O bound. With a fast
drive and a slow processor, you're processor bound.

If your system bottleneck is drive I/O and you write (with 2:1
compression) half the number of bytes, then it should take only half the
time for the writing. (Well, if there's a CRC check read-after-write
then the total write time might drop by one-third.)

Always trying to crank things up, I did install dual tape drives in one
of my machines a couple of years back. Both were Seagate 8GB (4GB
native), one was ATAPI and the other was SCSI. I was curious about the
speed improvement I'd get with SCSI. Ahahahahaha! The SCSI drive was
about 5% slower than the ATAPI drive. (Back Again/2, maximum
compression, Travan TR-4 tapes in both, Tekram DC-310 SCSI card w/ LSI
Logic chips, all hard drives were IDE.) Never did figure out why.

- Peter

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