Goswin von Brederlow wrote:

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.
  

That sounds a lot like what I mentioned, therefore it must be right. See 
the thread on sync on a new array, my reply to Neil.

-- 
Bill Davidsen [off-list ref]
  Even purely technical things can appear to be magic, if the documentation is
obscure enough. For example, PulseAudio is configured by dancing naked around a
fire at midnight, shaking a rattle with one hand and a LISP manual with the
other, while reciting the GNU manifesto in hexadecimal. The documentation fails
to note that you must circle the fire counter-clockwise in the southern
hemisphere.