dd performance on external hard drive

knappster · 11-01-2008, 06:18 AM

I've seen a lot of posts about dd for backing up dead hard drives, etc. I just used it to clear an external hard drive because Darik's Boot and Nuke does not work on external hard drives. I just wanted to post the results on this in case anybody wants to know how long it takes on external drives.

Note: I used the default block size.

Code:

dd if=/dev/urandom of=/dev/sdb

Quote:

dd: writing to `/dev/sdb': No space left on device
625142449+0 records in
625142448+0 records out
320072933376 bytes (320 GB) copied, 182781 seconds, 1.8 MB/s

For those of you who have not had math in a while, 182781 seconds = 50.7725 hours, which is just over 2 days. I just started another pass on the drive using a byte size of 1M, so I will post back with the results of it once it is completed (hopefully much quicker)

unSpawn · 11-01-2008, 07:15 AM

Check out frandom:

Code:

]# dd if=/dev/urandom of=/randfile bs=512 count=20000
10240000 bytes (10 MB) copied, 9.09083 seconds, 1.1 MB/s

]# dd if=/dev/frandom of=/randfile bs=512 count=20000
10240000 bytes (10 MB) copied, 0.924123 seconds, 11.1 MB/s

]# dd if=/dev/urandom of=/randfile bs=1M count=10
10485760 bytes (10 MB) copied, 8.73572 seconds, 1.2 MB/s

]# dd if=/dev/frandom of=/randfile bs=1M count=10
10485760 bytes (10 MB) copied, 0.504821 seconds, 20.8 MB/s

If you think fast can't be qualitatively good: just finish off writing some [PATTERN], then use your (forensic) tools to see if you can unearth something else than [PATTERN].

knappster · 11-01-2008, 09:41 PM

Hello unSpawn,

That sounds interesting. I am not that concerned about my data, I am RMAing a drive because the SATA data adapter broke, and I just wanted to do something a little better than formatting it to discourage anything. There's really nothing to hide on it anyway. But the results are:

Code:

dd bs=1M if=/dev/urandom of=/dev/sdb

Quote:

dd: writing `/dev/sdb': No space left on device
305246+0 records in
305245+0 records out
320072933376 bytes (320 GB) copied, 51600.7 seconds, 6.2 MB/s

14.3 hours is a pretty big improvement over 50+. I just thought maybe somebody would find this information useful.

unSpawn · 11-02-2008, 04:31 AM

Quote:

Originally Posted by knappster

14.3 hours is a pretty big improvement over 50+.

Then imagine how fast it would be using frandom. Maybe set it up and post results as comparison? After all setting up frandom only takes you 5 minutes if you have the kernel source for your current kernel available and configured...