Date: Sun, 01 Sep 2002 18:21:22 -0500 From: "Jack L. Stone" <jackstone@sage-one.net> To: Matthew Seaman <m.seaman@infracaninophile.co.uk>, 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: <3.0.5.32.20020901182122.014b5a00@mail.sage-one.net> In-Reply-To: <20020901230021.GC12421@happy-idiot-talk.infracaninophi> References: <Pine.BSF.4.21.0209011648400.13232-100000@wonkity.com> <20020901223639.GA12421@happy-idiot-talk.infracaninophi> <Pine.BSF.4.21.0209011648400.13232-100000@wonkity.com>
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At 12:00 AM 9.2.2002 +0100, 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
> 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
...and for the IDE as per Greg:
dd if=/dev/ad0c of=/dev/null bs=128k &
and in the background do an 'iostat ad0 1'. Here's an example with an
IDE drive:
=== grog@zaphod (/dev/ttyp0) ~ 3 -> iostat ad0 1
tty ad0 cpu
tin tout KB/t tps MB/s us ni sy in id
0 3 5.19 7 0.03 11 0 4 1 84
0 126 127.36 183 22.74 0 0 6 2 92
0 44 128.00 190 23.76 0 0 2 0 98
0 44 128.00 191 23.89 0 0 5 0 95
0 44 128.00 191 23.88 0 0 7 1 92
As you can see, it's really doing 128 kB transfers, for an average transfer
rate of almost 24 MB/s.
Best regards,
Jack L. Stone,
Administrator
SageOne Net
http://www.sage-one.net
jackstone@sage-one.net
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