Determine next snapshot size

[Ross_1976]

Hi all,
we haven't backed up a very large VM (2 TB) in a month and we'd like to know how large the next snapshot would be - compared to the latest reversed incremental file in the repository.
Our concern is to create a big snapshot which could potentially fill up the Vmware datastore. Is there a way / script to check the changed blocks against the latest .vrb file ?
Otherwise, we'd rather kick off a new Full which unfortunatelt will take hours to complete...
Thanks.

[tsightler]

It feels like you are mixing up a couple of different things here. The snapshot size is not impacted by the amount of change that exist since the last backup, only by the changes that will occur to the VM during the backup itself. Running a full and an incremental doesn't make any difference to the snapshot size at all, unless of course one runs significantly longer than the other. Basically, the longer the backup job runs, the larger the snapshot is likely to grow since it must store all of the change blocks while the backup itself is processing the base disk.

[Ross_1976]

Thanks Tom. This means that if we have , say, 100Gb of new data to be read and transferred, we won't ever see a 100Gb delta file in the datastore?

[tsightler]

The amount read and transferred has no impact, but if the VM gets 100GB of delta changes during the backup then the delta file could get that big.

[Vitaliy S.]

Our concern is to create a big snapshot which could potentially fill up the Vmware datastore.

What vSphere version are you at? I believe there was a way to redirect snapshot creation to the datastore that has sufficient free space for the snapshot.

Also in order to estimate the number of changes per day for this Exchange server, you can install Veeam ONE free edition. We have a predefined report template that can show you how much data is being changed on this Exchange server. Based on this value you can predict the size of the snapshot you're going to have during backup job run.