Date: Sun, 09 Mar 2003 00:49:36 +0000 From: "S W" <lordboink@hotmail.com> To: freebsd-questions@freebsd.org Subject: Re: dd *very* slow. Now 75x faster thanks to Kirk's suggestion! Message-ID: <F1410s4qJJs3ipjQPWV00046564@hotmail.com>
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..snip..
> I dropped that idea, but I'd read a post somewhere about dd, I tried...
>
> dd if=/dev/ad2 of=/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=/dev/zero of=/tmp/foo count=1
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=/dev/zero of=/tmp/foo count=1 bs=16384
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=/dev/ad2 of=/dev/da0 bs=512 count=16384
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.
--
Kirk Strauser
In Googlis non est, ergo non est.
<< attach3 >>
Here's the results of doubling the buffer size as you suggested:
BS bytes/sec
512 60808 (default)
1024 121614
2048 240212
4096 470312
8192 898897
16384 1652020
32768 2848452
65536 4490871*
131072 3811765
262144 3438026...
iostat now reports a steady 4+MB/s (75x increase).
Thanks alot, Kirk!
Boink
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