Date: Mon, 02 Sep 1996 14:49:19 -0700 From: "Michael L. VanLoon -- MindBender.serv.net" <michaelv@MindBender.serv.net> To: Michael Smith <msmith@atrad.adelaide.edu.au> Cc: bmcgloth@mail.vt.edu (Brian D. McGlothlin), freebsd-hardware@freebsd.org Subject: Re: DAT for sure! Message-ID: <199609022149.OAA28480@MindBender.serv.net> In-Reply-To: Your message of Tue, 03 Sep 96 00:27:29 %2B0930. <199609021457.AAA20616@genesis.atrad.adelaide.edu.au>
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>> An adaptec 1522 card (availability and win95 compatability)
>> and an HP C1534 2.0 GB 4mm DAT drive.
>Do _NOT_ buy a 1522. They're junk. If you have a PCI system of reasonably
>recent vintage with NCR SCSI support in the BIOS, get an NCR-810-based
[...]
>If you don't have PCI, then get an Adaptec 1540-series controller. A
>1540CP is probably your best bet.
Do _NOT_ buy a 154x unless you have exhausted all other bus types. If
you have an EISA bus, get an Adaptec 2742, or a BusLogic BT747. If
you have a VLB bus, get a BusLogic BT445 (or something that Adaptec
makes). You should _never_ settle for a 154x unless you have exhaused
all superior busses (or you already have one, it's free, and/or you
don't care if you have really slow SCSI performance).
Of course, if you have PCI, go that route first, with either an NCR
53c8xx card, like he describes, an Adaptec 2940 (or 2940UW), or a
BusLogic BT946 (or 956 [wide] or 948 [ultra] or 958 [ultra wide]).
>The issue here is that the 1522 is
>based on a really cheezy SCSI chip that requires lots of CPU
>attention, and thus delivers really poor performance. Both the 1540
>and the NCR-based controllers (the NCR will be cheaper, incidentally)
>do busmaster DMA, and reap all the rewards of real SCSI controllers.
And, even though the 1542 is fully bus-mastering, and is quite a bit
better performing than a 1522, it is still a sluggish non-performer
compared to better busses. The issue here is that the 154x runs in an
ISA bus. Remember, the ISA bus maxes out at 8MB/s, and that is
discounting all contention. In the real world, you'll be lucky to get
4-5MB/s. There are modern drives that can do that in a single drive.
Coupled with the fact that if you have more than 16MB of RAM, the OS
has to "bounce-buffer" data above 16MB (basically copy it back and
forth) to make it work on an ISA bus-mastering controller, further
degrading performance. Yes, it's better than a 1522, but it's still
close to the bottom of the ladder.
You will get vastly better performance with an EISA or VLB (though VLB
is kinda hit-and-miss) controller than you will with an ISA
controller.
-----------------------------------------------------------------------------
Michael L. VanLoon michaelv@MindBender.serv.net
--< Free your mind and your machine -- NetBSD free un*x >--
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NetBSD ports in progress: PICA, others...
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