Date: Sun, 1 Sep 2002 17:38:51 -0600 (MDT) From: Warren Block <wblock@wonkity.com> To: Matthew Seaman <m.seaman@infracaninophile.co.uk> Cc: FreeBSD LIST <FreeBSD-Questions@FreeBSD.ORG> Subject: Re: dd if=/dev/zero of=/dev/ad1 Message-ID: <Pine.BSF.4.21.0209011736520.13398-100000@wonkity.com> In-Reply-To: <20020901230021.GC12421@happy-idiot-talk.infracaninophi>
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On Mon, 2 Sep 2002, Matthew Seaman wrote: > On Sun, Sep 01, 2002 at 04:52:39PM -0600, Warren Block wrote: > > On Sun, 1 Sep 2002, Matthew Seaman wrote: > > > > > It's part of the IDE specification: 128k is the maximum IO transfer > > > size. Oh --- the equivalent figure for SCSI discs is 64kB. > > > > I'm reasonably certain that for SCSI it's 64K *blocks* of 512 bytes > > each, or 32M. Some systems may have driver limitations that break > > transfers up into 64K chunks, though. > > Like FreeBSD perhaps? > > happy-idiot-talk:/home/matthew:# dd if=/dev/da0c of=/dev/null bs=1m & > [2] 13192 > happy-idiot-talk:/home/matthew:# iostat da0 1 > tty da0 cpu > tin tout KB/t tps MB/s us ni sy in id > 5 11 0.00 0 0.00 2 0 0 3 94 > 1 43 64.00 556 34.77 1 0 2 2 95 > 0 43 64.00 557 34.84 1 0 0 4 95 Sure. The point being that with IDE, 128Kbyte transfers are a result of the hardware. With SCSI, 64Kbyte transfers are the result of the driver, not the hardware. -Warren Block * Rapid City, South Dakota USA To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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