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Re: [libvirt] [PATCH 2/2] Adjust block size used by dd to speed QEMU domain save operations.



On 06/04/2010 10:38 AM, Daniel P. Berrange wrote:
On Fri, Jun 04, 2010 at 08:23:32AM -0600, Eric Blake wrote:
In that case, it may be better to have two constants - the preferred
transfer size (1M), and the XML padding block size (512 as before, or
perhaps 4k given newer disk architectures that prefer 4k), along with
code that allows the final transfer to be shorter than the preferred
size so long as it is still a multiple of the block size.
That doesn't work because dd can't seek into the file a size less than
its transfer size. ie the seek=NN parameter is specifying a multiple
of the bs=XX value, not an absolute seek position in bytes.

Yup, very bothersome, but true. Maybe we should file a bug against dd ;-)

So do I have the ACK or can someone think of a straightforward way to avoid the wastage?


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