Re: mismatch_cnt again

Martin K. Petersen
2009-11-17T05:22:07Z

>>>>> "Goswin" == Goswin von Brederlow <goswin-v-b@web.de> writes:

>> I agree that making MD RAID1 do a copy would be a quick fix. But I
>> don't see any reason to encourage what is essentially sloppy behavior
>> at the top of the stack. And then what if you stack MD/DM devices?
>> Do each layer do a copy? I think that gets murky pretty quickly.

Goswin> Maybe as a quick debug the raid layer should make the page
Goswin> read-only and then watch what fails to write to it.

That's essentially what the fs-level debug patches do. The advantage is
that you get a bit more information about the call path when you do it
up there.

Goswin> Maybe a flag somewhere saying if the data is safe from writes or
Goswin> not. Default would be unsafe and md copies. A filesystem that
Goswin> works "right" sets the safe flag as would md after copying. That
Goswin> way anything lower in the stack (like another md) has the flag
Goswin> set.

I actually have a patch kicking around in my guilt stack that implements
such a flag. Mostly because it appears nobody is interested in fixing
ext2.

--
Martin K. Petersen Oracle Linux Engineering