Re: scp sparse dd file

[Pádraig Brady]

On 04/02/2012 10:30 PM, Simon Hintermann wrote:
> Hello all,
> 
> I have a tricky one (so do I think)...
> 
> My virtual machines are raw-based files, created with a "dd if=/dev/zero 
> of=.. bs=1M count=0 seek=120000", for example.
> 
> As I want to have native I/O performances on my servers, I do not use any NAS 
> or SAN, so when I want to migrate my VMs: scp and/or rsync.
> 
> Now is there any way to be able to copy a sparse dd file that uses only 10MB 
> out of 120GB without transferring the whole 120GB over to another server 
> (keeping the sparse capability, of course...)?
> 
> Thank you for your expertise!

Since cp --version 8.11, sparse files are read efficiently,
from file systems that support the fiemap system call (most modern ones).
cp has traditionally supported efficient writing of sparse files
through the use of seek() rather than write().

cheers,
Pádraig.