Re: [Qemu-devel] [RFC] live snapshot, live merge, live block migration

[Jagane Sundar]

Hello Dor,
> One important advantage of live snapshot over live backup is support of
> multiple (consecutive) live snapshots while there can be only a single
> live backup at one time.
>
> This is why I tend to think that although live backup carry some benefit
> (no merge required), the live snapshot + live merge are more robust
> mechanism.

The two things that concern me regarding the
live snapshot/live merge approach are:
1. Performance considerations of having
    multiple active snapshots?
2. Robustness of this solution in the face of
    errors in the disk, etc. If any one of the snapshot
    files were to get corrupted, the whole VM is
    adversely impacted.

The primary goal of Livebackup architecture was to have zero
performance impact on the running VM.

Livebackup impacts performance of the VM only when the
backup client connects to qemu to transfer the modified
blocks over, which should be, say 15 minutes a day, for a
daily backup schedule VM.

One useful thing to do is to evaluate the important use cases
for this technology, and then decide which approach makes
most sense. As an example, let me state this use case:
- A IaaS cloud, where VMs are always on, running off of a local
  disk, and need to be backed up once a day or so.

Can you list some of the other use cases that live snapshot and
live merge were designed to solve. Perhaps we can put up a
single wiki page that describes all of these proposals.

Thanks,
Jagane