On Wed, Feb 3, 2010 at 1:41 PM, Sampsa Riikonen <sampsa.riikonen@iki.fi> wrote: <snip>
- Per is using blocksize of 65536 bytes ~ 65 Mb
Thats 64KB not MB. And your command "dd if=/dev/sda of=/dev/sdb bs=X" should be dd if=/dev/sda of=/dev/sdb bs=X conv=noerror,sync noerror says to continue the copy even if there is a media error on the /dev/sda. sync says when that media error occurs replace the failed data with zeros (nulls). Without sync it just copies truncated data. Really bad because you won't be able to restore the now corrupted data at all. X is obviously important for performance, but it you go with 1MB and there is a read error you can end up with a full MB of missing data even though only one sector was actually bad. I have done a lot of benchmarking of this process. As a company that has 5 computers primarily dedicated to running the above command to duplicate our clients data for preservation / analysis we have chosen eSata with 4K blocks as our optimum solution. We get good throughput with minimal risk of data loss due to a bad sector. With fast eSata drives I've seen dd speeds approaching 4GB/min or 240GB/hr. But that is pretty rare and takes good fast drives. A lot of drives just can't deliver data that fast. FYI: We actually do something closer to dd if=/dev/sda of=/evidence_drive/computer_name.img bs=4K conv=noerror, sync The resulting file is called a dd forensic image and is the basis of many civil and criminal court actions. If you master typing in the above you have mastered the first step of being a computer forensic examiner. (There are lots of ways to create a forensic image, but the above really is how we do it.) disclaimer: The State of Georgia, USA says that if you use the above command to collect potential evidence for a paying client to use in a court case you have to have a PI license. Same for South Carolina. Why that makes sense I have no idea. Bet you never saw that disclaimer before!! Greg PI license # available upon request :) -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org