[Qemu-discuss] How to get progress while drive-backup

[Jin Ma]

version: qemu-2.9.0-16.el7_4.11



Hi, Can I get progress while doing drive backup?

backup command:

>> virsh qemu-monitor-command vm-name'{"execute":"drive-backup"
,"arguments": {....}}'



after I started backup, I tried "query-block-job" command (
https://wiki.qemu.org/Features/ImageStreamingAPI)

and use offset / len as percentage:

>> virsh qemu-monitor-command vm-name'{"execute":"query-block",
"arguments":{}}'

{
"return": [{
"io-status": "ok",
"device": "test-517",
"busy": true,
"len": 10485760,
"offset": 65535,
"paused": false,
"speed": 1024,
"ready": false,
"type": "backup"
}],
"id": "libvirt-195451"
}

note: len equals virtual size of qcow2



But it was not always accurate.

When backup mode is full, offset / len will walk from 0 to 100%, but much
more quickly when busy = false.

When backup mode is top, offset / len will start from 0, but will end up to
"actual size/virtual size" nearly rather than 100%

When backup mode is incremental, offset / len will start from somewhere and
end up somewhere, maybe 47% -> 48%.



I cared about the granularity and count of bitmap. But has not found out
the relations with incremental backup offset



Did I miss something?