On Tue, 04 Sep 2012 12:06:26 -0600 Chris Friesen <chris.friesen@genband.com>
wrote:

> 
> Hi,
> 
> I'm not really a filesystem guy so this may be a really dumb question.
> 
> We currently have an issue where we have a ~1TB RAID1 array that is 
> mostly given over to LVM.  If we swap one of the disks it will rebuild 
> everything, even though we may only be using a small fraction of the space.
> 
> This got me thinking.  Has anyone given thought to using the TRIM 
> information from filesystems to allow the RAID code to maintain a 
> bitmask of used disk blocks and only sync the ones that are actually used?
> 
> Presumably this bitmask would itself need to be stored on the disk.
> 
> Thanks,
> Chris
> 
> 

Something like this?
  http://neil.brown.name/blog/20110216044002#5

NeilBrown