Date: Thu, 01 Jun 1995 09:06:25 -0700 From: "Justin T. Gibbs" <gibbs@freefall.cdrom.com> To: Torbjorn Granlund <tege@matematik.su.se> Cc: bugs@FreeBSD.org Subject: Re: 3 problems using FreeBSD 2.0.950412-SNAP Message-ID: <199506011606.JAA23005@freefall.cdrom.com> In-Reply-To: Your message of "Thu, 01 Jun 95 17:05:46 %2B0200." <199506011505.PAA05866@insanus.matematik.su.se>
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>* Using an Adaptec 2940 and a Quantum Atlas 34301 (a 4.1GB fast SCSI-II > drive) I don't get more than 5MB/s. I actually get *exactly* 5MB/s for > large transfers. Since both the controller and the drive handles 10MB/s, > and the BIOS is set up properly, and the SCSI bus is terminated properly, > I would expect a sustained transfer rate of close to 10MB/s. The bus runs at 10Mhz which means 10MB/s during data transfers. You need to take into consideration bus arbitration, selection, reconnection, and message phases in order to get a more realistic number. My guess would be 8.5->9MB/s max on an 8bit, fast, bus. I don't have the drive specs on the Atlas handy, but just because it can run the bus at 10MHz doesn't mean it can dump data at that speed. You need to take into consideration the spindle speed, head possition, and data density. For example, the theoretical max on an Empire 2100 is 5.12MB/s. Now, this is not to say that there aren't improvements that can be made to the 2940 (aic7xxx) driver. There are quite a few things I have planned to improve transactional overhead (FreeBSD does does at most 64k in a transfer, so transactional overhead is important), but I'm much more interested in killing any and all compatibility problems with the sequencer code first. -- Justin T. Gibbs ============================================== TCS Instructional Group - Programmer/Analyst 1 Cory | Po | Danube | Volga | Parker | Torus ==============================================
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