Date: Wed, 26 Apr 2000 11:32:53 -0700 From: Kent Stewart <kstewart@3-cities.com> To: Matthew Dillon <dillon@apollo.backplane.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: <39073655.56A70C00@3-cities.com> References: <Pine.BSF.3.96.1000426165333.74116e-100000@haldjas.folklore.ee> <3907177C.5CFEC69A@3-cities.com> <200004261751.KAA96154@apollo.backplane.com>
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Matthew Dillon wrote: > > 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. But that depends on what is also going on at the same time. There are three other cards in my PCI bus. You can eliminate one because I wasn't using the sound card :). > > 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). This is where the cache size on the HD becomes important. It also acts like a hardware double buffering. > > 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. I haven't seen any 30MB/s. The 10K LVD IBM's were just about the fastest at 20MB/s continuous. The drop for UDMA drives is to even lower rates. > > So in the case of a file copy over a SCSI bus, the physical disk is > almost always going to be the limiting factor. I just noticed that mine isn't showing "Tagged Queueing Enabled" is that something I can set? The adapter is an Adaptec 2940uw. da0 at ahc0 bus 0 target 4 lun 0 da0: <IBM DCAS-34330W S65A> Fixed Direct Access SCSI-2 device da0: 40.000MB/s transfers (20.000MHz, offset 8, 16bit) da0: 4134MB (8467200 512 byte sectors: 255H 63S/T 527C) Kent -- Kent Stewart Richland, WA mailto:kstewart@3-cities.com http://www.3-cities.com/~kstewart/index.html FreeBSD News http://daily.daemonnews.org/ SETI(Search for Extraterrestrial Intelligence) @ HOME http://setiathome.ssl.berkeley.edu/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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