Re: [Qemu-devel] [RFC V3 0/9] Quorum disk image corruption resiliency

[Stefan Hajnoczi]

On Mon, Aug 20, 2012 at 12:42 PM, Benoît Canet <address@hidden> wrote:
>
> Le Monday 20 Aug 2012 à 12:24:33 (+0100), Stefan Hajnoczi a écrit :
>> On Mon, Aug 20, 2012 at 12:23 PM, Stefan Hajnoczi <address@hidden> wrote:
>> > On Mon, Aug 20, 2012 at 11:12 AM, Benoît Canet <address@hidden> wrote:
>> >> Le Tuesday 14 Aug 2012 à 16:14:02 (+0200), Benoît Canet a écrit :
>> >>> This patchset create a block driver implementing a quorum using m qemu 
>> >>> disk
>> >>> images. Writes are mirrored on the m files.
>> >>> For the reading part the m files are read at the same time and a vote is
>> >>> done to determine if a qiov version is present n or more times. It then 
>> >>> return
>> >>> this majority version to the upper layers.
>> >>> When i < n versions of the data are returned by the lower layer the
>> >>> quorum is broken and the read return -EIO.
>> >>>
>> >>> The goal of this patchset is to be turned in a QEMU block filter living 
>> >>> just
>> >>> above raw-*.c and below qcow2/qed when the required infrastructure will 
>> >>> be done.
>> >>>
>> >>> Main use of this feature will be people using NFS appliances which can be
>> >>> subjected to bitflip errors.
>> >>>
>> >>> This patchset can be used to replace blkverify and the out of tree 
>> >>> blkmirror.
>> >>>
>> >>> usage: -drive 
>> >>> file=quorum:n/m:image_1.raw:...:image_m.raw,if=virtio,cache=none
>> >>
>> >> stefanha: I am wondering what would be needed to do in order to have COR 
>> >> and streaming working
>> >> with quorum.c ?
>> >
>> > .bdrv_is_allocated()/.bdrv_co_is_allocated() needs to be supported by
>> > block/quorum.c.  Have you tried it and found a problem?
>>
>> Just want to confirm you are thinking about image streaming on top of
>> quorum?  Or are you thinking about streaming underneath quorum?
>
> I am thinking about streaming with quorum on top of a bunch of backing files.
> ie: data landing into the higher level backing file living just under quorum.

If there are backing files then there must be qcow2 or another image
format on top of quorum:

qcow2 ("virtio0")
+------ foo.img (file)
+------ quorum (backing_hd)
        +------- backing_a.img
        +------- backing_b.img
        +------- backing_c.img

.bdrv_is_allocated()/.bdrv_co_is_allocated() must be supported by quorum.

Stefan