Date: Sun, 2 Jul 2000 23:55:24 -0600 From: "Kenneth D. Merry" <ken@kdm.org> To: David Gilbert <dgilbert@velocet.ca> Cc: Kent Stewart <kstewart@3-cities.com>, freebsd-stable@FreeBSD.ORG Subject: Re: Dump takes ages on SCSI. (several times faster on IDE) Message-ID: <20000702235524.A19820@panzer.kdm.org> In-Reply-To: <14687.57741.726207.302060@trooper.velocet.net>; from dgilbert@velocet.ca on Sun, Jul 02, 2000 at 08:42:53PM -0400 References: <14687.42282.873585.2561@trooper.velocet.net> <395FB9EA.E3115939@3-cities.com> <14687.57741.726207.302060@trooper.velocet.net>
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On Sun, Jul 02, 2000 at 20:42:53 -0400, David Gilbert wrote: > >>>>> "Kent" == Kent Stewart <kstewart@3-cities.com> writes: > > >> I then noticed that the IDE would crashdump somewhere around 10 > >> times faster than the SCSI disk. > >> > >> Why? Can the SCSI speed be improved? > > Kent> It depends on what 2940 and what IDE drive you are talking > Kent> about. I have a Maxtor UDMA66 that is 20MB/s faster in some > > I don't think this explains it at all. It would appear that the SCSI > driver is running in some "extra safe" mode, or something. It has > 512M to write sequentually to a partition... and the counting on the > screen, we're looking at 2 to 3 seconds-per-megabyte (on a drive that > delivers write performance of about 10M/s in normal operation). > > Maybe what I should have said that the ratio of regular operation to > dump performance of the ide driver is about 1:1 while it's 10:1 for > the SCSI driver... why is this? When the da(4) driver does a dump, it uses the CAM transport layer's polled completion/action facility, xpt_polled_action(). It looks like there is a substantial delay (1ms) in that routine between poll intervals. If you'd like it to go faster, you'll most likely have to ask Justin about it. (i.e., I didn't write it.) Ken -- Kenneth Merry ken@kdm.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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