Date: Sat, 20 Feb 1999 15:55:24 -0700 (MST) From: "Kenneth D. Merry" <ken@plutotech.com> To: paulz@trantor.xs4all.nl (Paul van der Zwan) Cc: freebsd-current@FreeBSD.ORG Subject: Re: Slow seq. write on Seagate ST36530N Message-ID: <199902202255.PAA14705@panzer.plutotech.com> In-Reply-To: <199902201159.MAA01220@trantor.xs4all.nl> from Paul van der Zwan at "Feb 20, 1999 12:59: 5 pm"
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Paul van der Zwan wrote... > > Paul van der Zwan wrote... > > > > > > I am having some performance problems on my -current ( update last weekend) > > > I hooked up a new Seagate ST36530N yesterday ( connected to an Adaptec 2940U) > > Andreas Klemm has had similar trouble, as he pointed out. > > Can you check and see whether or not you have write caching turned on for > > your disk? I have seen problems with sequential writes that appear to be > > caused by conflicts between FreeBSD's caching policy and disk caching > > policies. These problems often go away when you disable write caching on a > > disk. > > > > The Write Cache Enable (WCE) bit is in mode page 8. To check it: > > > > camcontrol modepage -n da -u 1 -v -m 8 > > > > To edit the mode page: > > > > camcontrol modepage -n da -u 1 -v -m 8 -e > > > > Let me know whether that affects the problem at all. > > This did not improve anything , but I think I have found the couse. > In that modepage there is a DISC value which was 0 on the IBM and 1 on the > Seagate. I remembered a ' Enable disconnect' option in the Adaptec 2940 bios, > setting this to 'off' for both harddisks led to a huge performance increase on > the Seagate. If I also enable Ultra mode iozone write goes from 1.5 MB/s > to 12 MB/s ( a factor of 8 !!!). The 'DISC' bit in mode page 8 has nothing to do with disconnection. Here's the description of it from the SCSI-3 spec: ================ The discontinuity (DISC) bit, when one, requests that the device server continue the pre-fetch across time discontinuities, such as across cylinders (or tracks in an embedded servo device), up to the limits of the buffer, or segment, space available for the pre-fetch. When zero, the DISC requests that pre-fetches be truncated (or wrapped) at time discontinuities. ================ Ken -- Kenneth Merry ken@plutotech.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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