Date: Thu, 06 Mar 2003 21:46:43 -0600 From: Kirk Strauser <kirk@strauser.com> To: freebsd-questions@freebsd.org Subject: Re: dd *very* slow (0.5KB/s) from IDE to SCSI - longish Message-ID: <87llzrbzz0.fsf@strauser.com> In-Reply-To: <F73ovgyMok0MQdzcGlC00002b47@hotmail.com> ("S W"'s message of "Fri, 07 Mar 2003 03:03:51 %2B0000") References: <F73ovgyMok0MQdzcGlC00002b47@hotmail.com>
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At 2003-03-07T03:03:51Z, "S W" <lordboink@hotmail.com> writes:
> I dropped that idea, but I'd read a post somewhere about dd, I tried...
>
> dd if=3D/dev/ad2 of=3D/dev/da0
>
> ...now the IDE activity LED has been on solid for about 4hours
dd's performance is highly depending on the size of its buffers, which are
abysmally small (512 bytes) by default:
kirk@kanga:~$ dd if=3D/dev/zero of=3D/tmp/foo count=3D1
1+0 records in
1+0 records out
512 bytes transferred in 0.000074 secs (6916211 bytes/sec)
You can increase this by specifying your own buffer size:
kirk@kanga:~$ dd if=3D/dev/zero of=3D/tmp/foo count=3D1 bs=3D16384
1+0 records in
1+0 records out
16384 bytes transferred in 0.000173 secs (94654927 bytes/sec)
Before starting the full transfer, do something like:
dd if=3D/dev/ad2 of=3D/dev/da0 bs=3D512 count=3D16384
and keep doubling the size of the bs argument until the throughput values
stop increasing noticably, then use that value to duplicate your drive. It
will still be somewhat slow, but I guarantee you can speed it up by at least
5 times.
=2D-=20
Kirk Strauser
In Googlis non est, ergo non est.
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