Re: RAID5 reconstruction ?

On Sat, 2009-05-30 at 14:35 +0100, John Robinson wrote:

On 30/05/2009 06:44, SandeepKsinha wrote:

quoted

Hi all,

Say If I have a RAID 5 array of 50GB of five disks of 10GB each.

I have data of 5GB. When a disk fails and replaced with a spare disk.
Will the reconstruction happen only for the 5GB allocated disk blocks
or it will happen for the whole disk size.

The whole disc size, for now anyway; md does not currently note which 
blocks have been used by its client (the filesystem, LVM, whatever).

quoted

Is it possible to make  reconstruction intelligent enough to keep it optimized ?

This has been discussed in combination with supporting SSD drives' TRIM 
function, and would mean md had to keep track of used chunks or possibly 
even sectors using a bitmap or something like that, but whether anyone's 
working on it I don't know.

I would say it should be possible to 'query' the filesystem for that
information. Obviously this will only work if you run a filesystem on it
which supports it, but it would seem like a nicer solution than a bitmap
for it.

Cheers,

John.

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