Re: Copying Disk Drives with dd

[Marcin Cinik]

Use bs option (size of copy buffer).
For example:

dd bs=8M if=/root/file of=/dev/sdb8

Good idea would be to use compression to decrease size of backup file
dd bs=8M if=/root/file | gzip -9 > /mnt/foobar

where /mnt/foobar is /dev/sdb8 filesystem mounted on /mnt/foobar

Maybe You could also use some software which would clean up (write with
zeroes) unused disk space before backup. Size of compressed file would
shrink a lot then. I don't know such software at this moment. And
efficiency of such util will surely depend on filesystem You have
on /dev/sdb8

Marcin

On Wed, 2007-07-25 at 22:52 +0200, Janis Hamme wrote:
> Hello from Germany :)
> 
> I want to use the tool dd to create a backup of my hard disk. I have to 
> identical sata2 hard disks.
> 
> My idea was just to copy them using
>     dd if=/dev/sda of=/dev/sdb
> but the speed was terrible slow. Not more than ~ 15 MB/s.
> 
> In order to find the problem I copied a 1 GB file to partition sdb8. 
> Speed was about ~ 55 Mb/s. Seems good.
>     dd if=/root/file of=/dev/sdb8
> 
> Next I tried to copy the same file to the same partition with the command
>     dd seek=146818098 if=/root/file of=/dev/sdb
> Speed was only ~ 15 MB/s although the result was the same.
> It seems to be as slow as copying the whole disk.
> 
> I've made these tests with Knoppix and the Gentoo Live CD.
> 
> My Questions are:
>     - Why is the speed that slow?
>     - How can i speed it up without copying each partition.
> 
> Hope you are able to understand my problem (and my english).
> 
> Janis Hamme
> 
> 
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