Re: raid6 rebuild

[Bill Davidsen <davidsen@tmr.com>]

Lennert Buytenhek wrote:
> On Wed, Apr 04, 2007 at 08:22:00PM -0700, Dan Williams wrote:
>
>   
>>> While my RAID6 array was rebuilding after one disk had failed (which
>>> I replaced), a second disk failed[*], and this caused the rebuild
>>> process to start over from the beginning.
>>>
>>> Why would the rebuild need to start over from the beginning in this
>>> case?  Why couldn't it just continue from where it was?
>>>       
>> I believe it is because raid5 and raid6 share the same error handler
>> which sets MD_RECOVERY_ERR after losing any disk.  It should probably
>> not set this flag in 1-disk lost raid6 case, but I might be
>> overlooking something else.
>>     
>
> Right, so you're saying that it's probably a bug rather than an
> intentional 'feature'?

No, I would say it's a "reviewable design decision" To be pedantic (as I 
often am), a bug really means that unintended results are generated. In 
this case I think the code functions as intended, but might be able to 
safely take some other action.

I confess, I would feel safer with my data if the rebuild started over, 
I would like to be sure that when it (finally) finishes the data are 
valid. If you replaced the 2nd drive, then a full rebuild would be 
required in any case, to get ALL drives valid.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979