Re: online fsck

[Hans Reiser <reiser@namesys.com>]

Chris Mason wrote:

>On Thu, 2004-04-22 at 13:51, Hans Reiser wrote:
>  
>
>>Chris Mason wrote:
>>
>>    
>>
>>>On Thu, 2004-04-22 at 09:00, Jure Peèar wrote:
>>> 
>>>
>>>      
>>>
>>>>Hi all,
>>>>
>>>>Is it theoretically posible?
>>>>
>>>>Like, does it need a drastic redesing of reiserfs or just sufficient $$
>>>>directed to the team to be implemented?
>>>>
>>>>
>>>>Because i think that reiserfsck --check in 12h + --rebuild-tree in 18h is
>>>>still waaay too much downtime for a 500gb mail server...
>>>>   
>>>>
>>>>        
>>>>
>>>Online check is easy, just use lvm or evms to make a snapshot and then
>>>check the snapshot. 
>>>
>>>      
>>>
>>Requires that users use lvm before discovering the need for fsck, but, 
>>yes.  What would be ideal would be some support for finding the 
>>inconsistency on the snapshot, and then fixing it on the real fs using 
>>the information learned from the snapshot fsck.
>>    
>>
>
>Which should be possible, espeically for corruptions at the leaf
>levels.  Things like incorrect i_size, pointers to files that don't
>exist, etc.  Corruptions that require a full blow rebuild-tree will be
>much harder.
>
>I was wrong to say that an online rebuild-tree would be impossible, but
>it certainly does seem tricky.  Basically you could freeze the old tree,
>using it for readonly lookups.  Rebuild to new tree in the background,
>and verify things you find in the old tree in the new tree (to catch a
>file that has been deleted while the FS was mounted but is present in
>the old tree).
>
>-chris
>
>
>
>
>  
>
rebuild-tree would likely  be a major engineering effort which would 
require funding from someone who cared enough to pay for it....., 
finding inconsistencies on a snapshot and applying them to a live system 
would be less difficult but still substantive work.