Re: RAID5 reconstruction ?

[Redeeman <redeeman@metanurb.dk>]

On Sat, 2009-05-30 at 20:55 +0200, Goswin von Brederlow wrote:
> Redeeman <redeeman@metanurb.dk> writes:
> 
> > On Sat, 2009-05-30 at 14:35 +0100, John Robinson wrote:
> >> On 30/05/2009 06:44, SandeepKsinha wrote:
> >> > 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).
> >> 
> >> > 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.
> 
> And just when I hit send I thought of something else.
> 
> Instead of the initial sync when creating a raid the bitmap could just
> mark all blocks as unused. Much faster raid creation.

A filesystem-coexist mode could also do this, by simply refusing
operation until such a time that a filesystem is detected, or i suppose
in worst case, mounted...

> 
> MfG
>         Goswin
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