[SOLVED] slow dd? only 10.8 MB/s, I hoped for more

[phajdan.jr]

I used dd to copy disk partition contents, and this is the result:

[Randy Andy]

Hi phajdan.jr.

No you did nothing wrong, dd is not the fastest under the sun

Eventually you can improve it a little using a bigger block-size parameter like this way:

[frostschutz]

Default dd blocksize is just way too small (read 512 bytes, write 512 bytes, read ...), it has so much overhead that it doesn't use the full speed of the disk.

dd utilizes the full disk speed starting with a 100kb blocksize (run your own benchmarks though)

I use bs=1M because that way, the dd progress output (x records out etc.) is easiest to understand, as the number == the megabytes copied, no need to do any math to figure out how far along it is you can make it print the current progress with kill -SIGUSR1 `pidof dd`

Note that larger blocksize also has disadvantages, for example if the medium is defective you want a smaller blocksize (actual blocksize of your disk, so that's 512 bytes or with newer HDDs 4k), so it really only leaves out the defective blocks, and not a whopping 4MB (if you used 4MB blocksize). Note that for defective media you'll also need conv=noerror,sync to make it skip the defective blocks and zero their counterparts in the copy.

[phajdan.jr]

Thank you, using bs=4M worked great, and the resulting speed was about 50 MB/s.
_________________
http://phajdan-jr.blogspot.com/