Symptoms:

An administrator may see different values presented in Zerto UI and when browsing the VMware datastores. This also relates to Journal volumes.
This article will explain where the differences are coming from.

Cause:

Presented in Zerto UI:
The Recovery data size is as following:
- Calculated Used Recovery Storage:  This is not exactly the value received from VC but an internal calculation based on that.
- Calculated Journal used size: For each VM, the ZVM will go over all of the recovery volumes and count their allocated segments in the journal.

The reason is coming from the fact that Zerto actually might not fully use all the segments (due to VRA behavior).

In other words, it is unlikely that Calculated journal used size will be equal to the actual used space of the journal.
The differences can be a couple of MBs per volume(which can add up to hundreds of MB).