Date: Mon, 2 Sep 2002 00:00:21 +0100 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: Warren Block <wblock@wonkity.com> Cc: Matthew Seaman <m.seaman@infracaninophile.co.uk>, FreeBSD LIST <FreeBSD-Questions@FreeBSD.ORG> Subject: Re: dd if=/dev/zero of=/dev/ad1 Message-ID: <20020901230021.GC12421@happy-idiot-talk.infracaninophi> In-Reply-To: <Pine.BSF.4.21.0209011648400.13232-100000@wonkity.com> References: <20020901223639.GA12421@happy-idiot-talk.infracaninophi> <Pine.BSF.4.21.0209011648400.13232-100000@wonkity.com>
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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
0 42 64.00 556 34.74 0 0 2 3 95
0 43 64.00 557 34.82 0 0 1 3 96
Cheers,
Matthew
--
Dr Matthew J Seaman MA, D.Phil. 26 The Paddocks
Savill Way
Marlow
Tel: +44 1628 476614 Bucks., SL7 1TH UK
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