Re: [Qemu-devel] [RFC 00/12] Qorum disk image corruption resiliency

[Benoît Canet]

Le Friday 03 Aug 2012 à 16:14:51 (+0000), Blue Swirl a écrit :
> On Thu, Aug 2, 2012 at 10:16 AM, Benoît Canet <address@hidden> wrote:
> > This patchset create a block driver implementing a qorum using three qemu 
> > disk
> > images. Writes are mirrored on the three files.
> > For the reading part the three files are read at the same time and a vote is
> > done to determine which is the majoritary qiov version. It then return this
> > majoritary version to the upper layers.
> > When three differents versions of the data are returned by the lower layer 
> > the
> > qorum is broken and the read return -EIO.
> 
> It would be pretty easy to make the number of nodes and quorum
> threshold values for both read and write selectable. Then you could
> have for example 100 nodes and write quorum at 51 (for example, 49
> nodes offline). Obviously writing the same data 100 times sequentially
> would not give very high performance but it's a start.

For now the number of disk is hardcoded to 3. But most of the code is written
with a variable number of disk in mind: just quorum_open and quorum_vote would 
need
to be rewritten with a few automatic changes across the code.