Re: [Qemu-devel] [PATCH COLO v4 00/15] Block replication for continuous checkpoints

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Wen Congyang (wency@cn.fujitsu.com) wrote:
> Block replication is a very important feature which is used for
> continuous checkpoints(for example: COLO).
> 
> Usage:
> Please refer to docs/block-replication.txt
> 
> You can get the patch here:
> https://github.com/wencongyang/qemu-colo/commits/block-replication-v4
> 
> You can get the patch with the other COLO patches here:
> https://github.com/wencongyang/qemu-colo/tree/colo_huawei_v4.7

Hi,
  A couple of questions:
     1) I still trip the handle_aiocb_rw assertion occasionally;
  I see Kevin was asking for some detail on http://lists.nongnu.org/archive/html/qemu-devel/2015-01/msg04507.html
     is that still the right fix?

     2) The only stats I see on the block replication are the info block-jobs
        completed 'n' of 'm' - is 'n' there just the total number of blocks written?
        Are there any more stats about?


> TODO:
> 1. Test failover when the guest does too many I/O operations. If it
>    takes too much time, we need to optimize it.

Limiting the size of the state needed for commit might help that; you can
always trigger a new checkpoint if the size gets too big; it would also
make it more realistic since it will probably fail at the moment if you
fill up the RAM you're using to hold the hidden/active disks with a big
write.

Dave

> 2. Continuous block replication. It will be started after basic functions
>    are accepted.
> 
> Changs Log:
> V4:
> 1. Introduce a new driver replication to avoid touch nbd and qcow2.
> V3:
> 1: use error_setg() instead of error_set()
> 2. Add a new block job API
> 3. Active disk, hidden disk and nbd target uses the same AioContext
> 4. Add a testcase to test new hbitmap API
> V2:
> 1. Redesign the secondary qemu(use image-fleecing)
> 2. Use Error objects to return error message
> 3. Address the comments from Max Reitz and Eric Blake
> 
> Wen Congyang (15):
>   docs: block replication's description
>   allow writing to the backing file
>   Allow creating backup jobs when opening BDS
>   block: Parse "backing_reference" option to reference existing BDS
>   Backup: clear all bitmap when doing block checkpoint
>   Don't allow a disk use backing reference target
>   Add new block driver interface to connect/disconnect the remote target
>   NBD client: implement block driver interfaces to connect/disconnect
>     NBD server
>   Introduce a new -drive option to control whether to connect to remote
>     target
>   NBD client: connect to nbd server later
>   Add new block driver interfaces to control block replication
>   skip nbd_target when starting block replication
>   quorum: implement block driver interfaces for block replication
>   quorum: allow ignoring child errors
>   Implement new driver for block replication
> 
>  block.c                    | 270 +++++++++++++++++++++++-
>  block/Makefile.objs        |   3 +-
>  block/backup.c             |  13 ++
>  block/nbd.c                |  67 ++++--
>  block/quorum.c             | 142 ++++++++++++-
>  block/replication.c        | 512 +++++++++++++++++++++++++++++++++++++++++++++
>  blockdev.c                 |   8 +
>  blockjob.c                 |  10 +
>  docs/block-replication.txt | 179 ++++++++++++++++
>  include/block/block.h      |  10 +
>  include/block/block_int.h  |  18 ++
>  include/block/blockjob.h   |  12 ++
>  qapi/block.json            |  16 ++
>  qemu-options.hx            |   4 +
>  tests/qemu-iotests/051     |  13 ++
>  tests/qemu-iotests/051.out |  13 ++
>  16 files changed, 1260 insertions(+), 30 deletions(-)
>  create mode 100644 block/replication.c
>  create mode 100644 docs/block-replication.txt
> 
> -- 
> 2.1.0
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK