Re: Major design flaw with BTRFS Raid, temporary device drop will corrupt nodatacow files

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2018年06月28日 10:10, Remi Gauvin wrote:
> On 2018-06-27 09:58 PM, Qu Wenruo wrote:
>>
>>
>> On 2018年06月28日 09:42, Remi Gauvin wrote:
>>> There seems to be a major design flaw with BTRFS that needs to be better
>>> documented, to avoid massive data loss.
>>>
>>> Tested with Raid 1 on Ubuntu Kernel 4.15
>>>
>>> The use case being tested was a Virtualbox VDI file created with
>>> NODATACOW attribute, (as is often suggested, due to the painful
>>> performance penalty of COW on these files.)
>>
>> NODATACOW implies NODATASUM.
>>
> 
> yes yes,, none of which changes the simple fact that if you use this
> option, which is often touted as outright necessary for some types of
> files, BTRFS raid is worse than useless,, not only will it not protect
> your data at all from bitrot, (as expected), it will actively go out of
> it's way to corrupt it!
> 
> This is not expected behaviour from 'Raid', and I despair that seems to
> be something that I have to explain!

Nope, all normal raid1 is the same, if you corrupt one copy, you won't
know which one is correct.
Btrfs csum is already doing much better job than plain raid1.

Please get yourself clear of what other raid1 is doing.

Thanks,
Qu


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