Date: Sun, 21 Feb 1999 00:26:26 +0100 From: Paul van der Zwan <paulz@trantor.xs4all.nl> To: "Kenneth D. Merry" <ken@plutotech.com> Cc: freebsd-current@FreeBSD.ORG Subject: Re: Slow seq. write on Seagate ST36530N Message-ID: <199902202326.AAA73531@trantor.xs4all.nl> In-Reply-To: Your message of "Sat, 20 Feb 1999 15:55:24 MST." <199902202255.PAA14705@panzer.plutotech.com>
next in thread | previous in thread | raw e-mail | index | archive | help
> > > > 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. > ================ I did not change it but it triggered me to have a look at the Adaptec BIOS settings. I have done some testing and reenabled disconnection, preformance dropped to less than 2MB/s writing. After searching the freebsd-scsi archives I found out it might be related to tagging, so I edited /usr/src/sys/cam/cam_xpt.c and added an entry to disallow tagging for this drive. Back to 12 MB/s. So it looks like there is at least an acceptable ( to me ) workaround. Maybe the CAM maintainer can put an entry in cam_xpt.c for this drive ??? dmgs shows is as : da1 at ahc0 bus 0 target 1 lun 0 da1: <SEAGATE ST36530N 1444> Fixed Direct Access SCSI-2 device da1: 20.000MB/s transfers (20.000MHz, offset 15) da1: 6208MB (12715920 512 byte sectors: 255H 63S/T 791C) Paul -- Paul van der Zwan paulz @ trantor.xs4all.nl "I think I'll move to theory, everything works in theory..." To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199902202326.AAA73531>