Date: Sun, 16 Jun 1996 21:00:18 -0700 From: "Justin T. Gibbs" <gibbs@freefall.freebsd.org> To: Beck Peccoz Amedeo <gea@masternet.it> Cc: freebsd-current@FreeBSD.ORG Subject: Re: ahc syncing questions Message-ID: <199606170400.VAA10485@freefall.freebsd.org> In-Reply-To: Your message of "Sun, 16 Jun 1996 16:24:21 %2B0200." <31C41915.41C67EA6@masternet.it>
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>Justin T. Gibbs wrote: > > I've got a Seagate wide HD (ST32550W) acceptinc max sync transfer >rate of 20 Mbytes/s (i.e. 10MHz). Don't confuse the issue. It syncs at a clock rate measured in MHz not MB/s. >If I set the ultra speed on the adapter >(20MHz or 40Mb/s) it still syncs at 10MHz. So far so good. Right since it can't do 20MHz. If you have an old version of the driver, you may actually be syncing at 5MHz though. I fixed the Ultra bug about a month or so ago. > 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. Ha. That drive will not get anywhere near 16MB/s. 16Mb/s I might believe (2MB/s). To figure out the maximum you can expect from the drive, you need to look at media transfer rates, not the sync rate. A quick calculation using the RPM of the drive and its media density should get you what you want. Remember that the driver transfers short bursts of data across the SCSI bus at the negotiated sync rate, but in most cases it cannot sustain that rate throughout the entire transfer. >-- > >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 > > -- Justin T. Gibbs =========================================== FreeBSD: Turning PCs into workstations ===========================================
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