On Tue, 04 Sep 2012 15:11:26 -0400 Ric Wheeler <ricwheeler@xxxxxxxxx> wrote: > On 09/04/2012 02:06 PM, Chris Friesen 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 > > > > Device mapper has a "thin" target now that tracks blocks that are allocated or > free (and works with discard). > > That might be a basis for doing an focused RAID rebuild, I wonder how.... Maybe the block-later interface could grow something equivalent to "SEEK_HOLE" and friends so that the upper level can find "holes" and "allocated space" in the underlying device. I wonder if it is time to discard the 'block device' abstraction and just use files every .... but I seriously doubt it. NeilBrown
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