Date: Mon, 08 May 1995 18:32:00 -0700 From: "Justin T. Gibbs" <gibbs@estienne.CS.Berkeley.EDU> To: Tom Samplonius <tom@haven.uniserve.com> Cc: Scott Mace <smace@metal-mail.neosoft.com>, hackers@FreeBSD.org Subject: Re: Is a 486 fast enough for SCSI? Message-ID: <199505090132.SAA03301@estienne.cs.berkeley.edu> In-Reply-To: Your message of "Mon, 08 May 1995 15:34:11 PDT." <Pine.BSF.3.91.950508152847.717C-100000@haven.uniserve.com>
next in thread | previous in thread | raw e-mail | index | archive | help
>
>On Mon, 8 May 1995, Scott Mace wrote:
>
>> > I've got a AMD486DX4100 with an Adaptec 2940 and two SCSI drives. When
>> > I run iozone on one drive I get about 1.9MB/s, but when I run a iozone on
>> > each drive I get about .9 MB/s (roughly half). Since the SCSI bus runs
>> > at 10MB/s per second, the limiting factor appears to be the CPU? I
>> > thought PCI devices required very little CPU time?
>> >
>>
>> The limiting time is the speed of the drive. I can get over 3megs/sec
>> with my EISA bt747 and seagate barracuda drives. And my cpu is only
>> a 486DX2-66. I'm never seen a single scsi drive actually do 10MB/sec.
>
> I realize that no SCSI drive can do 10MB/s, but it is clearly not the
>bottleneck when accessing two drives simultaneously, so what is?
>
>Tom
I'm not sure since I don't have the same hardware. On my 2742 card, with
a Quantum Empire 2100 and a Quantum PD1225 running "iozone 128 8192":
Empire 2100 with the 1225 also doing an iozone:
3491843 bytes/second for writing the file
3106667 bytes/second for reading the file
Emprire 2100 by itself.
4900133 bytes/second for writing the file
5204443 bytes/second for reading the file
The first set of number looks a little low, but I'd have to play around
with some of the bus timing numbers to get a better idea of just how bad
they are. It isn't a 50% reduction though.
--
Justin T. Gibbs
==============================================
TCS Instructional Group - Programmer/Analyst 1
Cory | Po | Danube | Volga | Parker | Torus
==============================================
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199505090132.SAA03301>