[7485] in linux-scsi channel archive
Fast copy
daemon@ATHENA.MIT.EDU (Douglas Gilbert)
Wed Nov 3 23:51:24 1999
Message-ID: <38210EAB.37E40B90@interlog.com>
Date: Wed, 03 Nov 1999 23:42:19 -0500
From: Douglas Gilbert <dgilbert@interlog.com>
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To: linux-scsi@vger.rutgers.edu
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While testing out a new sg driver, I have stumbled across
an impressive speed-up in disk to disk copy times. This may
only be on my hardware but I hope others can get similar
results on their equipment.
The timed test involves copying one disk to another. Both disks
are IBM model DCHS04U which hold 4.4 GB each and have average
continuous streaming rates of about 9 MB/sec (on both reads and
writes). The test is the elapsed time that a copy takes:
# dd if=/dev/sda of=/dev/sdb bs=512
This took about 30 minutes. Bypassing buffering and using the
sg interface with "sg_dd" brought this time down to 24 minutes.
Using another variant called sgq_dd that queues both reads and
writes asynchronously brought this time down to 9 minutes 20
seconds.
Just reading a disk and throwing away the result takes about
8 minutes 50 seconds (i.e. "dd if=/dev/sda of=/dev/null").
Paying an extra 30 seconds to write that 4.4 GBytes to
another disk seems like a pretty good deal.
There is more information at:
http://www.torque.net/sg [follow fast copy link]
Are there other Linux/Unix utilities that give this type of
performance?
Doug Gilbert
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