This consists of these 1.3 features:

* A new block job is supported: live disk mirroring (also known as "storage migration") moves data from an image to another. A new command "block-job-complete" is used to switch the VM to use the destination image exclusively.

* QEMU embeds an NBD server, accessible via the monitor. The NBD server allows live access to the image seen by the VM. Note that the embedded server uses "named exports", which QEMU can access using the "nbd://host:port/name" syntax. 

* The monitor now remains responsive during incoming migration. The new NBD server is also available during incoming migration.

====

For testing, the process should be as follows:

1) Optionally, copy the base images from the source machine to the destination disk.

2) Create empty images on the destination disk, using "qemu-img create".  Point them to the base images copied in step 1, if that step was done.

3) Start the destination QEMU and sets up the NBD server using the nbd-server-start and nbd-server-add commands.

 { "execute": "nbd-server-start", "arguments": {
   "addr": { "type": "inet",
             "data": { "host": "10.34.56.78", "port": "12345" } } } }

 { "execute": "nbd-server-add", "arguments": {
   "addr": { "device": "drive-virtio0", "writable": true" } }

 { "execute": "nbd-server-add", "arguments": {
   "addr": { "device": "drive-ide0-hd0", "writable": true" } }

 etc.

4) Invoke drive-mirror on the source, once for each migrated disk, with a destination pointing to the remote NBD server.  URI syntax can be used for drive-mirror's target argument, for example nbd://10.34.56.78:12345/diskname (where diskname is the -drive id specified on the destination).  Use "sync: 'top'" if the base images exist on the destination, "sync: 'full'" otherwise.

The format must _always_ be raw!  This is independent of the format of the disk on the source.

 { "execute": "drive-mirror",
   "arguments": { "device": "drive-ide-hd0",
                  "target": "nbd://10.34.56.78:12345/drive-virtio0",
                  "sync": "full", "format": "raw" } }

 { "execute": "drive-mirror",
   "arguments": { "device": "drive-ide-hd0",
                  "target": "nbd://10.34.56.78:12345/drive-ide0-hd0",
                  "sync": "full", "format": "raw" } }

5) once all mirroring jobs reach steady state, invoke the migrate command.

6) once migration completes, quit the source QEMU and invoke the nbd-server-stop command on the destination QEMU.

 { "execute": "nbd-server-stop", "arguments": { } }

All steps can also be executed via the human monitor too.  The commands are named with underscores instead of dashes, however.

Hi Paolo,

After i execute:

 { "execute": "nbd-server-add", "arguments": {
   "addr": { "device": "drive-virtio0", "writable": true" } }

qmp connection get stuck without return, however, i test hmp cmd, it works.

I am not sure there is a bug or just wrong cmd, i notice it misses a " in front of true, but this is not the problem. I look into qmp-command.hx, finding the instuction is different from our rhel6 internal version in qemu-monitor.hx:


{ 'command': 'nbd-server-start',
  'data': { 'addr': 'SocketAddress' } }

{ 'command': 'nbd-server-add', 'data': {'device': 'str', '*writable': 'bool'} }


Is this the upstream style or sth new? I can not tell what the final qmp cmd i should use from this, and now our internal qemu-kvm-rhel7 tree simply bases on upstream 1.3, so a little tips would be great.

That's a typo, sorry:

 { "execute": "nbd-server-add",
   "arguments": { "device": "drive-virtio0", "writable": true" } }

That's a typo, sorry:

 { "execute": "nbd-server-add",
   "arguments": { "device": "drive-virtio0", "writable": true } }

(In reply to comment #5)
> That's a typo, sorry:
> 
>  { "execute": "nbd-server-add",
>    "arguments": { "device": "drive-virtio0", "writable": true } }

Remove the ", the command still hangs, won't return.

Current status:

1. on des host, after issue qmp command "nbd-server-add", qmp connection hangs, command won't return:

{ "execute": "nbd-server-start", "arguments": { "addr": { "type": "inet", "data": { "host": "10.66.71.224", "port": "3333" } } } }
{"return": {}}
{ "execute": "nbd-server-add", "arguments": { "addr": { "device": "drive-virtio-disk0", "writable": true } }

2. instead, on des host, use HMP command to add block, it works:

nbd_server_add -w drive-virtio-disk0

3. on src host, start mirroring:

{ "execute": "drive-mirror", "arguments": { "device": "drive-virtio-disk0", "target": "nbd://10.66.71.224:3333/drive-virtio-disk0", "sync": "full", "format": "raw", "mode": "existing" } }

4. after reaching steady state, do migration, it finishes correctly.


Functionally works fine, the only problem is qmp nbd-server-add command won't return.

Verified on qemu-kvm-rhev-1.5.3-31.el7.x86_64:

CMD:

on des host:

{ "execute": "qmp_capabilities" }
{"return": {}}

{ "execute": "nbd-server-start", "arguments": { "addr": { "type": "inet", "data": { "host": "10.66.5.84", "port": "3333" } } } }
{"return": {}}

{ "execute": "nbd-server-add", "arguments": { "device": "drive-virtio-disk0", "writable": true } }
{"return": {}}

on src host:

{ "execute": "qmp_capabilities" }
{"return": {}}

{ "execute": "drive-mirror", "arguments": { "device": "drive-virtio-disk0", "target": "nbd://10.66.5.84:3333/drive-virtio-disk0", "sync": "full", "format": "raw", "mode": "existing" } }
{"return": {}}

This request was resolved in Red Hat Enterprise Linux 7.0.

Contact your manager or support representative in case you have further questions about the request.