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

[Takahiro Yasui <tyasui redhat com>]

On 06/25/09 10:47, Mikulas Patocka wrote:
>> superblock approach may solve this data corruption issue without an
>> additional delay. When dm-raid1 detects a write error, it can disable
>> the mirror leg quickly and ask userspace to process aftertreatment.
>>
>> I would like to continue discussion how to fix this issue.
>>
>> Thanks,
>> Taka
> 
> The current code already blocks all i/os if the log fails. So if your 
> application is sensitive for it, you have to test for it anyway.

It is also a known issue. We are trying to make a log device redundant
to prevent disk replication when a log device has problem. It will
solve the delay caused by a log device failure as well.

> You can write new implementation dm-raid1.2 that will have two log devices 
> (just like md-raid has two superblocks) and can perform without userspace 
> intervention if any of the legs or logs fail.
> 
> But it is really more like rewrite --- I think it would be easier to write 
> it from scratch than to patch it over existing dm-raid1 code.

Hmm. I will look at implementation if we could add superblocks into
current code.

Thanks,
Taka