Is your application generating more data this week than it did last week? Has something suddenly changed? Has a user suddenly decided to fill up their VM's local filesystem with uncompressible contraband media content? Has somebody turned on guest-side disk or filesystem encryption, causing a big drop in data compressibility on the storage side?
It's easy to notice things like this when you have per-VM snapshots; all you have to do is look at the size of the incremental snapshots (daily or hourly) and see literally how much new data a VM generated in a given day.
In the field
Recently we had an interesting case where it was necessary for a customer to replicate a 10TB virtual machine between two data centers approximately 1000 miles apart. The network bandwidth available was approximately 80Mbps. How long would it take to replicate such a VM?
Calculating this answer was straightforward. First, we looked at the post-compressed size of the VM. This is possible because the Tintri filesystem calculates the post-compressed size of the VM's live data as well as its snapshots. It doesn't matter what the compression rate of the overall system is; that might vary significantly from the compression rate for the data in any one particular VM.
And, because Tintri VM replication also compresses the data in transit, the sum of the compressed size of the VM's snapshots indicates how much total data will have to transfer over the network. Tintri's VM replication also utilizes deduplication, but in this case we made no assumption that any of the VM's data would be found on the destination.
Here is the data on this VM's snapshots, taken directly from the VMstore UI on the customer's replication source system: