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From: Mikhail Teterin <mi@aldan.algebra.com>
Message-Id: <199807230339.XAA17390@rtfm.ziplink.net>
Subject: ccd questions
To: questions@FreeBSD.ORG
Date: Wed, 22 Jul 1998 23:39:29 -0400 (EDT)
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Hello!

I'm trying to do this under a day old -stable. There are four disks
-- 2 2Gb and 2 4Gb -- involved. I set up two ccd mirroring disks
2Gb and 4Gb big each with different ileave numbers (from 2 to 6000,
being powers of 2 and primes). Here are my problems:

The 4 disks are on an ahc of their own with an idle tape-drive. I
never tested both arrays at the same time. The 3 system disks are
on a separate ahc. The machine has a single PPro-200 with 256Kb of
cache, 128Mb of RAM, 192Mb of swap split evenly among three system
drives.

Performance:

	All four disks are different, so I do not expect "optimum"
	performance, but my results were still disappointing :(

	According to iozone benchmark, the write speed went down 50%
	compared to when using the disks by themselves -- without
	ccd. I would expect it to stay the same, really -- it is
	about 3.5Mb/sec and is far from saturating the 10Mb/s top
	of this SCSI interface. The ileave number does not seem to
	matter once it is above 32.

	The read speed is about the same -- according to `systat 1
	-iostat' the data is read only from the first disk of an
	array -- I'd expect it to double as the things can be read
	in parallel from each of the drives. Again the ileave number
	does not seem to matter once it is above 32.


Features/stability:

	I tried to create the third ccd to concatenate the two
	mirroring disks into one 6Gb big chunk. It "did not work"
	most of the time, and crashed the system once when it seemed
	to succeed and I started to
		newfs /dev/rccd2c
	Is this combination supposed to work at all?

Thanks for your comments and suggestions! Yours,

	-mi

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