On Mon, Aug 20, 2012 at 3:03 PM, Benoît Canet <benoit.ca...@irqsave.net> wrote:
> Le Monday 20 Aug 2012 ŕ 13:56:53 (+0100), Stefan Hajnoczi a écrit :
>> On Mon, Aug 20, 2012 at 12:42 PM, Benoît Canet <benoit.ca...@irqsave.net>
>> wrote:
>> >
>> > Le Monday 20 Aug 2012 ŕ 12:24:33 (+0100), Stefan Hajnoczi a écrit :
>> >> On Mon, Aug 20, 2012 at 12:23 PM, Stefan Hajnoczi <stefa...@gmail.com>
>> >> wrote:
>> >> > On Mon, Aug 20, 2012 at 11:12 AM, Benoît Canet
>> >> > <benoit.ca...@irqsave.net> wrote:
>> >> >> Le Tuesday 14 Aug 2012 ŕ 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.
>
> This seems like a low hanging fruit.
>
> Too bad we cannot create new snapshot of quorum file easily without full
> block filter support in qemu.
> Am I right ?
If the snapshot also needs to use quorum then we definitely need more
logic during the snapshot creation process than exists today.
Stefan
