Re: [Qemu-devel] [PATCH v5 0/3] Quorum maintaince operations

[Benoît Canet]

The Friday 30 May 2014 à 19:53:12 (+0200), Max Reitz wrote :
> On 30.05.2014 13:18, Benoît Canet wrote:
> >These are the last bits required to make quorum usable in production.
> >
> >v5:     rebase on latest Stefan's block branch [Kevin]
> >
> >v4:
> >         update patchset to stefan's block branch
> >                 drop Max reviewed by because the series changes
> >
> >Benoît Canet (3):
> >   quorum: Add the rewrite-corrupted parameter to quorum.
> >   block: Add drive-mirror-replace command
> >   qemu-iotests: Add 096 new test for drive-mirror-replace.
> 
> Independently of this series, while looking at patch 1 again
> (although I had reviewed it before already), I noticed that
> quorum_get_winner() does not select the definite winner, but only a
> winner. So if you have a quorum instance with four children and a
> threshold of two, it may happen that there are basically two winners
> which both fulfill the threshold condition. In this case,
> quorum_get_winner() will just return the first winner. However, I
> think it should then return that there is no winner (i.e., NULL).
> 
> On the other hand, the user should be aware that it may be a bad
> idea to choose a threshold which does not exceed half of the
> children count; thus, I'm just asking what you think about this. :-)

I think Quorum n/(2 *n) is a bad idea. (n + 1) / (2 *n) is a least required.

I wonder where we could put some documentation about this for the user.

Best regards

Benoît

> 
> Max
>