Date: Sun, 19 Jan 1997 00:31:09 -0600 (CST) From: "Daniel M. Eischen" <deischen@iworks.InterWorks.org> To: md3547@mclink.it, questions@freebsd.org Subject: Re: SCSI-III support Message-ID: <199701190631.AAA07065@iworks.InterWorks.org>
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> a few weeks ago I have bought the FreeBSD CD-ROM from Walnut Creek (vers. 2.1.5). > Today I have been told by my PC reseller that they cannot provide the 2GB Fast > SCSI-II disk for the PC I have just ordered. Instead, they could replace the > AHA 2940 PCI SCSI controller adapter with the newer AHA 2940 AU and a 2GB SCSI > -III disk. I wonder if the ahc0 driver that is in FreeBSD 2.1.5 can drive that > configuration. The PC will be ready at the end of next week and I really need to > know it asap - I'm buying it just to run FreeBSD! Can you please help me? > > Thanks a lot in advance, FreeBSD 2.1.5-RELEASE does not support the 2940AU, but FreeBSD 2.1.6 and subsequent do support the 2940AU. I'd let your reseller give you the SCSI-III disk (ultra), but I might think twice about getting the 2940AU vs the 2940. The 2940AU has only 3 SCBs, while the 2940 has 16 SCBs. Even though the 2940AU can do Ultra mode transfers (up to 20 MHz), with only 3 SCBs it isn't going to buy you as much as having 16 SCBs. The FreeBSD aic7xxx driver has a paging algorithm for paging in and out SCBs to/from sequencer RAM. There's some bugs with the paging algorithm right now, but even when it's working there is some overhead involved. I'd see if you could squeeze out a 2940U or 2940UW from your reseller. Both of these controllers have 16 SCBs like the 2940, and they can do Ultra transfers too. To learn more about the paging algorithm, which will allow up to 255 SCBs to be used, see sys/i386/scsi/aic7xxx.c. The aic7xxx author wrote a nice little description about the paging algorithm. Dan Eischen deischen@iworks.InterWorks.org
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