Re: RAID5 reconstruction ?

[Maxime Boissonneault <maxime.boissonneault@usherbrooke.ca>]

John Robinson a écrit :
> 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 don't know how it goes for Linux, but hasn't ZFS been developped 
exactly for that purpose ? From what I understand, ZFS manage both the 
file system and the RAID features at once. Therefore, the "raid" part 
knows where are the files and the filesystem knows about the raid. 
Reconstruction is then done intelligently (not reconstructing unused space).


Maxime Boissonneault

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