On Sun, May 31, 2009 at 1:07 AM, Redeeman [off-list ref] wrote:

On Sat, 2009-05-30 at 20:55 +0200, Goswin von Brederlow wrote:

quoted

Redeeman [off-list ref] writes:

quoted

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

quoted

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.

quoted

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.

This really sounds like a good option. This would have a slight hit
for writes which I believe will compensate for later re-constructions,
replacing a disk, mirror resysnc and many more operation.

Neil any comments on this?

I mean, how difficult would it be to maintain such a bitmap. This can
though of making something optional as this will incur space.

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...

quoted

MfG
        Goswin
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-- 
Regards,
Sandeep.





 	
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