Date: Wed, 26 Apr 2000 10:51:02 -0700 (PDT) From: Matthew Dillon <dillon@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) Message-ID: <200004261751.KAA96154@apollo.backplane.com> 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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