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From: se@zpr.uni-koeln.de (Stefan Esser)
Date: Sat, 7 Oct 1995 22:43:47 +0100
In-Reply-To: Bruce Evans <bde@zeta.org.au>
       "Re: VLB Disk Controllers" (Oct  8,  7:15)
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To: Bruce Evans <bde@zeta.org.au>
Subject: Re: VLB Disk Controllers
Cc: se@sysiphos.mi.uni-koeln.de
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On Oct 8,  7:15, Bruce Evans wrote:
} 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?

NCR 53c810 (driven by a 486DX2/66):

Command overhead is 751 usec (time_4096 = 1216, time_8192 = 1682)
transfer speed is 8.79954e+06 bytes/sec

Seems that even at 4KB, the NCR is a lot faster than an IDE controller :)

Let's see:

IDE: 512/1815890 s + 573 us = 855 us
NCR: 512/8799540 s + 751 us = 809 us

Seems the NCR is faster on 512 byte transfers.
Now I guess this is not really a "large i/o" :)

Regards, STefan

-- 
 Stefan Esser, Zentrum fuer Paralleles Rechnen		Tel:	+49 221 4706021
 Universitaet zu Koeln, Weyertal 80, 50931 Koeln	FAX:	+49 221 4705160
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 http://www.zpr.uni-koeln.de/staff/esser/esser.html	  <se@ZPR.Uni-Koeln.DE>