Alexey D. wrote:Trevor, it also reminds that "Safe snapshot removal option" should mostly be used with pre-ESX 3.5 U2 hosts.
I see Veeam reps state this a lot, but I actually think this option is still valuable even for newer versions. It's true that VMware versions 3.5 U2 and later use a snapshot removal method that is very similar to "safe snapshot removal" anyway, but for some reason it's not quite the same. I think when VMware is removing snapshots it still "throttles" the guest OS somewhat, probably to attempt to limit growth of the new snapshot. We see this on our Exchange server quite noticably if a backup/replication is preform during a busy portion of the day.
As an example, if a Veeam backup is run on our Exchange server, and takes 30-40 minutes, we can easily end up with 6-8GB of snapshots that have to be removed. Because the Exchange server is still very busy while snapshot removal is taking place, it can take anywhere from 60-90 minutes for VMware to complete removing the snapshot. During the time users get very poor performance, and mail can sometimes become backlogged.
If we use "safe snapshot removal", it takes even longer to remove the snapshot, but for some reason the impact on users is almost unnoticed. I don't know for sure why Veeam's method of safe snapshot removal allows for more performance than VMware's native method, but it appears that VMware restricts the performance of the VM to try to make sure it is making progress in removing that snap, while Veeam doesn't have this side effect. We've had some success mitigating the impact of VMware's snapshot removal process by setting very high reservations for potentially busy VM's, but it's not a huge difference.