Date: Thu, 23 Jul 1998 13:38:31 +0930 From: Greg Lehey <grog@lemis.com> To: Mikhail Teterin <mi@aldan.algebra.com>, questions@FreeBSD.ORG Subject: Re: ccd questions Message-ID: <19980723133831.P8993@freebie.lemis.com> In-Reply-To: <199807230339.XAA17390@rtfm.ziplink.net>; from Mikhail Teterin on Wed, Jul 22, 1998 at 11:39:29PM -0400 References: <199807230339.XAA17390@rtfm.ziplink.net>
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On Wednesday, 22 July 1998 at 23:39:29 -0400, Mikhail Teterin wrote: > 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. Yes, I'd consider this result disappointing as well. May I assume that the performance improved with increasing the ileave factor? My investigations suggest that 128 is about the optimum, though there's not much improvement beyond 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. This would only happen if you're runnning multiple processes. Otherwise you'll be single-threaded by the test. > 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? I'm not sure what you're trying to do here. What does your /etc/ccdconfig look like? Are you trying to join ccds together into second-level ccds? I don't see any reason to want to do this, and I'm pretty sure nobody expects it to work. In any case, when you have such problems, there's little anybody can do without a kernel dump. You might like to try vinum (http://www.lemis.com/vinum.html) and see how that compares. Bear in mind, though, that this is still pre-release software. You shouldn't use it on production systems. Greg -- See complete headers for address and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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