On Thu, Jul 23, 2020 at 11:03:55AM +0300, Denis Plotnikov wrote: > > > On 22.07.2020 19:30, Peter Xu wrote: > > On Wed, Jul 22, 2020 at 06:47:44PM +0300, Denis Plotnikov wrote: > > > > > > On 22.07.2020 18:42, Denis Plotnikov wrote: > > > > > > > > On 22.07.2020 17:50, Peter Xu wrote: > > > > > Hi, Denis, > > > > Hi, Peter > > > > > ... > > > > > > How to use: > > > > > > 1. enable background snapshot capability > > > > > > virsh qemu-monitor-command vm --hmp migrate_set_capability > > > > > > background-snapshot on > > > > > > > > > > > > 2. stop the vm > > > > > > virsh qemu-monitor-command vm --hmp stop > > > > > > > > > > > > 3. Start the external migration to a file > > > > > > virsh qemu-monitor-command cent78-bs --hmp migrate exec:'cat > > > > > > > ./vm_state' > > > > > > 4. Wait for the migration finish and check that the migration > > > > > > has completed state. > > > > > Thanks for continued working on this project! I have two high level > > > > > questions > > > > > before dig into the patches. > > > > > > > > > > Firstly, is step 2 required? Can we use a single QMP command to > > > > > take snapshots > > > > > (which can still be a "migrate" command)? > > > > With this series it is required, but steps 2 and 3 should be merged into > > > > a single one. > > I'm not sure whether you're talking about the disk snapshot operations, > > anyway > > yeah it'll be definitely good if we merge them into one in the next version. > > After thinking for a while, I remembered why I split these two steps. > The vm snapshot consists of two parts: disk(s) snapshot(s) and vmstate. > With migrate command we save the vmstate only. So, the steps to save > the whole vm snapshot is the following: > > 2. stop the vm > virsh qemu-monitor-command vm --hmp stop > > 2.1. Make a disk snapshot, something like > virsh qemu-monitor-command vm --hmp snapshot_blkdev drive-scsi0-0-0-0 > ./new_data > 3. Start the external migration to a file > virsh qemu-monitor-command vm --hmp migrate exec:'cat ./vm_state' > > In this example, vm snapshot consists of two files: vm_state and the disk > file. new_data will contain all new disk data written since [2.1.] executing.
But that's slightly different to the current interface of savevm and loadvm which only requires a snapshot name, am I right? Now we need both a snapshot name (of the vmstate) and the name of the new snapshot image. I'm not familiar with qemu image snapshots... my understanding is that current snapshot (save_snapshot) used internal image snapshots, while in this proposal you want the live snapshot to use extrenal snapshots. Is there any criteria on making this decision/change? Thanks, -- Peter Xu
