On Tue, Mar 07, 2017 at 10:30:30PM +0800, Hailiang Zhang wrote: > Hi Stefan, > > Sorry for the delayed reply. > > On 2017/2/28 1:37, Stefan Hajnoczi wrote: > > On Fri, Jan 20, 2017 at 11:47:59AM +0800, zhanghailiang wrote: > > > Just as the scenario of non-shared disk block replication, > > > we are going to implement block replication from many basic > > > blocks that are already in QEMU. > > > The architecture is: > > > > > > virtio-blk || > > > .---------- > > > / || > > > | Secondary > > > / || > > > '---------- > > > / || > > > virtio-blk > > > / || > > > | > > > | || > > > replication(5) > > > | NBD --------> NBD (2) > > > | > > > | client || server ---> hidden disk > > > <-- active disk(4) > > > | ^ || | > > > | replication(1) || | > > > | | || | > > > | +-----------------' || | > > > (3) |drive-backup sync=none || | > > > --------. | +-----------------+ || | > > > Primary | | | || backing | > > > --------' | | || | > > > V | | > > > +-------------------------------------------+ | > > > | shared disk | <----------+ > > > +-------------------------------------------+ > > > > > > 1) Primary writes will read original data and forward it to Secondary > > > QEMU. > > > 2) The hidden-disk is created automatically. It buffers the original > > > content > > > that is modified by the primary VM. It should also be an empty > > > disk, and > > > the driver supports bdrv_make_empty() and backing file. > > > 3) Primary write requests will be written to Shared disk. > > > 4) Secondary write requests will be buffered in the active disk and > > > it > > > will overwrite the existing sector content in the buffer. > > > > > > Signed-off-by: zhanghailiang <zhang.zhanghaili...@huawei.com> > > > Signed-off-by: Wen Congyang <we...@cn.fujitsu.com> > > > Signed-off-by: Zhang Chen <zhangchen.f...@cn.fujitsu.com> > > > > Are there any restrictions on the shared disk? For example the -drive > > cache= mode must be 'none'. If the cache mode isn't 'none' the > > secondary host might have old data in the host page cache. The > > While do checkpoint, we will call vm_stop(), in which, the bdrv_flush_all() > will be called, is it enough ? > > > Secondary QEMU would have an inconsistent view of the shared disk. > > > > Are image file formats like qcow2 supported for the shared disk? Extra > > In the above scenario, it has no limitation of formats for the shared disk. > > > steps are required to achieve consistency, see bdrv_invalidate_cache(). > > > > Hmm, in that case, we should call bdrv_invalidate_cache_all() while > checkpoint.
Yes, it's not enough to just call bdrv_drain_all()/bdrv_flush_all(). The Secondary may need to reread metadata that is loaded in memory (e.g. qcow2's L2 table cache) so bdrv_invalidate_cache() is needed. Stefan
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