Re: RFC: use TRIM data from filesystems to speed up array rebuild?

[Ric Wheeler <ricwheeler@xxxxxxxxx>]

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,

Ric

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