From owner-freebsd-hackers  Wed Apr 26 10:51:11 2000
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Date: Wed, 26 Apr 2000 10:51:02 -0700 (PDT)
From: Matthew Dillon <dillon@apollo.backplane.com>
Message-Id: <200004261751.KAA96154@apollo.backplane.com>
To: Kent Stewart <kstewart@3-cities.com>
Cc: Narvi <narvi@haldjas.folklore.ee>,
	Michael Bacarella <mbac@nyct.net>,
	Alfred Perlstein <bright@wintelcom.net>,
	Kevin Day <toasty@dragondata.com>, hackers@FreeBSD.ORG
Subject: Re: Double buffered cp(1)
References: <Pine.BSF.3.96.1000426165333.74116e-100000@haldjas.folklore.ee> <3907177C.5CFEC69A@3-cities.com>
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    The standard PCI bus can do 130 MBytes/sec.  Even with overhead issues
    (setup for a DMA burst) it can still do 100 MBytes/sec.

    A standard SCSI controller can do 40, 80, and now even 160 MBytes/sec
    over the wire - standard copper cabling w/ LVD connectors (example 
    below).

    A modern hard disk can do 10-30 MBytes/sec to/from the platter, assuming
    no seeks.  But the moment it needs to seek the performance drops 
    drastically ... generally down to 1-5 MBytes/sec.

    So in the case of a file copy over a SCSI bus, the physical disk is
    almost always going to be the limiting factor.

						-Matt

da0 at ahc0 bus 0 target 0 lun 0
da0: <SEAGATE ST34573LW 6246> Fixed Direct Access SCSI-2 device 
da0: 80.000MB/s transfers (40.000MHz, offset 15, 16bit), Tagged Queueing Enabled
      ^^^^
da0: 4340MB (8888924 512 byte sectors: 255H 63S/T 553C)

da1 at ahc2 bus 0 target 0 lun 0
da1: <SEAGATE ST118273LW 6246> Fixed Direct Access SCSI-2 device 
da1: 40.000MB/s transfers (20.000MHz, offset 15, 16bit), Tagged Queueing Enabled
da1: 17366MB (35566480 512 byte sectors: 255H 63S/T 2213C)
da2 at ahc2 bus 0 target 1 lun 0
da2: <SEAGATE ST118273LW 6246> Fixed Direct Access SCSI-2 device 
da2: 40.000MB/s transfers (20.000MHz, offset 15, 16bit), Tagged Queueing Enabled
da2: 17366MB (35566480 512 byte sectors: 255H 63S/T 2213C)
Mounting root from ufs:/dev/da0s1a



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