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Old 3rd October 2008
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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?
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Old 3rd October 2008
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Quote:
Originally Posted by Carpetsmoker View Post
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
use raw devices (rwdxx) instead of block devices (wdxx), and use a larger blocksize (default is a measly 512 bytes), e.g.:
# dd if=/dev/rwd1c of=/dev/rwd0c bs=32k
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Last edited by wilfried; 3rd October 2008 at 08:12 AM.
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Old 3rd October 2008
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Quote:
Originally Posted by Carpetsmoker View Post
Why is dd so slow?
Try accessing the devices as character (raw) devices instead of block devices:

# dd if=/dev/rwd1c of=/dev/rwd0c
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Old 3rd October 2008
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About dd(1) bs size I always get best results with bs=8-16MB
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Old 3rd October 2008
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Alright, I already used ghost now to clone this drive, but I'll remember your tips for the next time, many thanks.
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