From owner-freebsd-current Sun Jun 16 06:55:48 1996 Return-Path: owner-current Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id GAA09001 for current-outgoing; Sun, 16 Jun 1996 06:55:48 -0700 (PDT) Received: from masternet.it (root@masternet.it [194.184.65.2]) by freefall.freebsd.org (8.7.5/8.7.3) with SMTP id GAA08993 for ; Sun, 16 Jun 1996 06:55:40 -0700 (PDT) Received: from socrate (ts1port15d.masternet.it [194.184.65.37]) by masternet.it (8.6.12/8.6.9) with SMTP id OAA28422; Sun, 16 Jun 1996 14:53:31 +0200 Message-ID: <31C41915.41C67EA6@masternet.it> Date: Sun, 16 Jun 1996 16:24:21 +0200 From: Beck Peccoz Amedeo X-Mailer: Mozilla 2.01 (X11; I; FreeBSD 2.2-CURRENT i386) MIME-Version: 1.0 To: "Justin T. Gibbs" CC: freebsd-current@FreeBSD.ORG Subject: Re: ahc sincing questions References: <199606160635.XAA19559@freefall.freebsd.org> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-current@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk Justin T. Gibbs wrote: > > While starting up the kernel with the -v option the ahc driver > >reports the sinc speed for any attached scsi device in MHz. > >Shouldn't be in Mbytes/s? > > MHz is correct. The sync rate is a measure of the clock rate at > which data is transfered. Only when you multiply that by the bus > width, do you get MBytes/s. Ok, I see. > > Why I see no difference when enable the ultra speed? My HD can > >sinc at 20 Mbytes/s, but it actually sincs only at 10... what's > >wrong? > > If you have a Wide drive, it does 10Mhz sync on a 16bit bus. If you > have an 8bit device, it must do 20Mhz sync in order to do 20MB/s. > What is your drive model? The only Ultra drive I know of on the market > is a Seagate one, and the person who tried it said it refused to negotiate > 20Mhz sync (looking from a SCSI bus analyzer) and that it was the device's > fault and not the driver's. I've got a Seagate wide HD (ST32550W) acceptinc max sync transfer rate of 20 Mbytes/s (i.e. 10MHz). If I set the ultra speed on the adapter (20MHz or 40Mb/s) it still syncs at 10MHz. So far so good. A problem arises when I run a benchmark, a very silly one, that does only read a big unfragmented file, as I get a transfer rate of only 7.4 Mb/s, while I read of a test on the same drive/adapter leading to a transfer rate of 16Mb/s, more than twice. It seems that the HD only negotiates at 10Mb/s, and as the ahc reports 10MHz either one of theese value is wrong or the wide channel is only used as a normal 8 bit one. -- Beck-Peccoz Amedeo GEA Software S.r.l. Via Deffeyes, 1 11025 Gressoney Saint Jean (AO) ITALY Tel. ++39-125-366302 Fax. ++39-125-366415