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Old 3rd October 2008
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Carpetsmoker Carpetsmoker is offline
Real Name: Martin
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Default dd slow, 1500KB/s (OpenBSD LiveCD)

Yesterday I wanted to clone a 500GB disk, this disk was somewhat faulty (Trouble spinning up, but once it was spinning it worked fine) and wanted to clone all data to an identical disk, dd is the obvious way to do that.

I booted jggmi's OpenBSD 4.3.1 liveCD, and used:
# dd if=/dev/wd1c of=/dev/wd0c

vmstat and systat show the speed to be about 1500 KB/s (!), this would mean it would take ~90 hours for the disk to be cloned (!).
I let dd run for well over 8 hours, and the speed didn't vary much, after I ^C-ed dd it told me the average speed was 1442010 bytes/sec.

I rebooted the machine, started Windows PE, used Norton Ghost, and the disk was cloned in about 30 minutes (As it should be).

Did I do something wrong? Why is dd so slow?
UNIX was not designed to stop you from doing stupid things, because that would also stop you from doing clever things.
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