From owner-freebsd-hackers Wed Apr 26 11:33:27 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from corinth.bossig.com (corinth.bossig.com [208.26.239.66]) by hub.freebsd.org (Postfix) with ESMTP id 5873A37B95C for ; Wed, 26 Apr 2000 11:33:22 -0700 (PDT) (envelope-from kstewart@3-cities.com) Received: from 3-cities.com (unverified [208.26.241.99]) by corinth.bossig.com (Rockliffe SMTPRA 4.2.1) with ESMTP id ; Wed, 26 Apr 2000 11:37:41 -0700 Message-ID: <39073655.56A70C00@3-cities.com> Date: Wed, 26 Apr 2000 11:32:53 -0700 From: Kent Stewart Organization: Columbia Basin Virtual Community Project X-Mailer: Mozilla 4.72 [en] (Windows NT 5.0; U) X-Accept-Language: en MIME-Version: 1.0 To: Matthew Dillon Cc: Narvi , Michael Bacarella , Alfred Perlstein , Kevin Day , hackers@FreeBSD.ORG Subject: Re: Double buffered cp(1) References: <3907177C.5CFEC69A@3-cities.com> <200004261751.KAA96154@apollo.backplane.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG 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: 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