[DRBD-user] Possible to force QuickSync?

Curtis Tiffany curtis at reecemarketing.com
Mon Mar 15 21:34:43 CET 2004


Björn Stenberg wrote:
> Philipp Reisner wrote:
> 
>>No there is no way to force a QuickSync. ( If we had it, its name
>>would be --shoot-myself-into-the-foot )
> 
> 
> Apologies if this has been discussed before, but I couldn't find it with google.
> 
> Has there been any discussion about the possibility of trading bandwidth for cpu by calculating and comparing checksums of disk blocks, thus only syncing modified blocks?

Yes.  The reason it's not been done so far is because disk i/o is 
usually the bottleneck, which isn't helped by using checksums.

It would probably be beneficial over long distance, lower speed links 
where disk i/o is not the bottleneck, but I haven't read anything that 
indicates anyone is working on this.

I believe the 7.x versions of drbd will have implement 'in use extents' 
that will help to avoid full syncs if possible and only transfer the 
blocks that have been updated.  That's the way I understand what they're 
working on...



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