Date: Sat, 16 Oct 1999 00:09:29 +0200 (MET DST) From: Gerard Roudier <groudier@club-internet.fr> To: "Kenneth D. Merry" <ken@kdm.org> Cc: "Chris D. Faulhaber" <cdf.lists@fxp.org>, Andrew Gallatin <gallatin@cs.duke.edu>, scsi@FreeBSD.ORG Subject: Re: FreeBSD 3.2 / Slow SCSI Dell PowerEdge 4300 Message-ID: <Pine.LNX.3.95.991015234921.543A-100000@localhost> In-Reply-To: <199910151940.NAA51114@panzer.kdm.org>
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On Fri, 15 Oct 1999, Kenneth D. Merry wrote: > Gerard Roudier wrote... > > On Fri, 15 Oct 1999, Chris D. Faulhaber wrote: > > > > > da0: <WDIGTL WDE9100 1.50> Fixed Direct Access SCSI-2 device > > > da0: 40.000MB/s transfers (20.000MHz, offset 8, 16bit) > > > da0: 8683MB (17783204 512 byte sectors: 255H 63S/T 1106C) > > > > > > After enabling tagged queuing on this drive (by removing the quirk entry) > > > and found performance about 10% slower. > > > > What kind of performance are you measuring ? Tagged command queuing is > > intended to improve _multithreaded IOs that is a lot more realistic IO > > pattern than single-threaded sequential IO. I also read some decrease of > > performance for DCAS for single-threaded sequential IO when increasing > > number of tags. Unless, guys, you just want to eat the cake and to have > > it, I donnot see any serious problem for these drives. May-be there is > > some room for improvement in their firmware. They should _not_ have been > > quirked to 0 tags, in my opinion, if the decrease of performance observed > > is for sequential IOs. At most, user should be advised to use a > > reasonnable number of tags or the quirk should have been more soft. > > > > For the DCAS, the decrease of performances has been observed for > > sequential write IOs that is a great stress for a disk when write behing > > caching is enabled with tags enabled, but still nothing has been reported > > for read and especially multithreaded read IOs. Castrating a disk model > > regarding tags due to such unreaslistic results has been unserious in my > > opinion. > > In the case of the DCAS drives, the PR author (see kern/10398) did > extensive tests with bonnie, and found that both the number of random seeks Random IO decrease is surprising given the small number of transactions per second and the small IO bandwidth needed for the test. Anyway, such a testing just makes the drive prefetch data and then makes it have to throw prefetched data away. Using simultaneous sequential IO streams may take advantage of the prefetching (such a testing is more realistic than Bonnie seeks). Some simple combination of usual UNIX commands is sometimes a far better testing than inappropriate benchmarks. > per second and sequential write throughput decreased as the number of > concurrent transactions allowed increased. Sequential read performance > did not vary significantly when the number of tags was changed. > As for the WD drives, if you'd like to find someone with a drive who is > willing to run through a full set of tests at various numbers of transactions, > feel free. If you can show that the number of tags should be set to > something other than 0, we can change it. I donnot know of WD drives and will probably never know about :-), but just based on the postings, I just thought that these drives were not proven to deserve a so severe punishment. Gérard. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the messagehelp
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