On Wed, Feb 3, 2010 at 5:04 AM, Herbert Graeber
Am 03.02.2010 10:52, schrieb Sampsa Riikonen:
[...]
I am trying to do a backup using
dd if=/dev/sda of=/dev/sdb
[...] What I read from wikipedia, the speed of that is..
60 Mbytes (not bits) per second ~ 0.06 Gbytes per second
So this means that a 500 Gbytes hard disk should copy in aprox. 2.3 hours
.. but know it seems it takes more than 24 hours!
What seems to be the problem? Am I missing something in the math?
Yes, you have to use a larger block size "dd if=/dev/sda of=/dev/sdb bs=1M" should speed up your backup.
My external usb hard disk box has also an option to use an esata connector (but then I should buy an adaptor to my laptop), but the speed difference to usb 2.0 is not that big, I imagine..?
As far as I know esata can be much faster, but to get the higher speed, you have to use larger block sizes, too.
I do this a lot and have run benchmarks. With raw disks (/dev/sda, etc) even a 512 byte blocksize works surprisingly well / efficiently But if your destination is a file on a filesystem, then 512 bytes can be horrible. 4K is the minimum to use in this case. Over 4K actually does very little to improve speed if your destination is a hdd. If your destination is a tape drive, you want big blocks. 1 MB or bigger would be reasonable. Also instead of dd, the mbuffer program is great for pulling a lot of data into ram (think a GB or more if you have the ram) and getting it ready to send to the tape in a large continuous stream. mbuffer is in 11.2, not sure about earlier. Having a continuous stream of data can drastically increase the speed of tape. Greg -- Greg Freemyer Head of EDD Tape Extraction and Processing team Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer Preservation and Forensic processing of Exchange Repositories White Paper - http://www.norcrossgroup.com/forms/whitepapers/tng_whitepaper_fpe.html The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org