Re: RAID5 reconstruction ?

[Bill Davidsen <davidsen@tmr.com>]

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.
>   

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 <davidsen@tmr.com>
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