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From: "Kenneth D. Merry" <ken@rflab1.gtri.gatech.edu>
Message-Id: <199510072313.TAA00822@rflab1.gtri.gatech.edu>
Subject: Re: VLB Disk Controllers
To: bde@zeta.org.au (Bruce Evans)
Date: Sat, 7 Oct 1995 19:13:38 -0400 (EDT)
Cc: hackers@freebsd.org
In-Reply-To: <199510072115.HAA03150@godzilla.zeta.org.au> from "Bruce Evans" at Oct 8, 95 07:15:24 am
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> That's not saying much. An IDE controller has a much lower command
> overhead than the buslogic:
> 
> Buslogic BT44C on 486DX2/66 VLB TOSHIBA MK537FB (slow disk):
> Output for disklatency /dev/rsd0:
> Command overhead is 4741 usec (time_4096 = 5164, time_8192 = 5586)
> transfer speed is 9.6955e+06 bytes/sec
> 
> Buslogic BT44C on 486DX2/66 VLB (QUANTUM XP34301 (fast disk):
> output for disklatency /dev/rsd1:
> Command overhead is 3968 usec (time_4096 = 4295, time_8192 = 4622)
> transfer speed is 1.25286e+07 bytes/sec
> 
> Cheap IDE on 486DX/33 ISA SAMSUNG SHD-3212A (slow disk):
> output for disklatency /dev/rwd0:
> Command overhead is 573 usec (time_4096 = 2830, time_8192 = 5087)
> transfer speed is 1.81489e+06 bytes/sec
> 
> A high command overhead causes slow file system operations for
> everything except large i/o's.
> 
> What are the command overheads of other popular controllers?

	Well, here's my go at it:

Adaptec 2842 on a i486DX4/100 VLB (QUANTUM XP34300) (Atlas, fast disk)
output for disklatency /dev/rsd0:
Command overhead is 567 usec (time_4096 = 1002, time_8192 = 1438)
transfer speed is 9.40748e+06 bytes/sec

	Oh yeah, my bus speed is 33 MHz, if that makes any difference.
And I was running X, and some other stuff at the time...



Ken
--
Kenneth Merry
ken@rflab1.gtri.gatech.edu
Disclaimer:  I don't speak for GTRI, GT, or Elvis.