If you're feeling kind, could you try and see if you could get a performance curve related to the number of outstanding tags allowed?
On Sun, 21 Feb 1999, Paul van der Zwan wrote: > > > > > > 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 majord...@freebsd.org > with "unsubscribe freebsd-current" in the body of the message > To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-current" in the body of the message
