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Re: [dm-devel] DM-RAID1 data corruption

Mikulas Patocka wrote:
>>> Of course, we can do something in the log itself but it will not fix
>>> "corelog" mirrors, more over the system can't auto recover after a
>>> missing log alone.
>> Yes, storing information on the log device does not save "corelog"
>> mirrors, so we might need some area to keep information on mirror
>> legs.
>> Thanks,
>> Taka
> MD-RAID1 solves this problem by having counters in superblocks on both 
> legs. If some leg dies, the counter on the other devices is increased. If 
> the dead disk comes online again, it is found that it has old counter and 
> cannot be trusted.
> Would it be possible to extend a logical volume when converting it to a 
> raid1 and use the last area of the volume as a superblock?

I agree with this idea. lvm metadata is managed by counters and I think
this method would work for this issue as well.

In addition, I think this sort of superblock is necessary not only
for fixing the data corruption issue but also for introducing faster
blockage algorithm which disables failed mirror legs in kernel.


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