Re: [PATCH 1/2] md bitmap bug fixes

[Paul Clements <paul.clements@steeleye.com>]

Peter T. Breuer wrote:
> Paul Clements <paul.clements@steeleye.com> wrote:

> I don't see that this solves anything. If you had both sides going at
> once, receiving different writes, then you are sc&**ed, and no
> resolution of bitmaps will help you, since both sides have received
> different (legitimate) data. It doesn't seem relevant to me to consider 

You're forgetting that journalling filesystems and databases have to 
replay their journals or transaction logs when they start up.


> What about when A comes back up? We then get a 
> 
>                  .--------------.
>         system A |    system B  |
>           nbd ---'    [raid1]   |
>           |           /     \   |
>        [disk]     [disk]  [nbd]-'
> 
> situation, and a resync is done (skipping clean sectors). 

You're forgetting that there may be some data (uncommitted data) that 
didn't reach B that is on A's disk (or even vice versa). That is why 
you've got to retrieve the bitmap that was in use on A and combine it 
with B's bitmap before you resync from B to A (or do a full resync).

--
Paul