I don't see any issues with this approach particularly if you are doing a snapshot just 5 minutes prior to the VSS sync'd snapshot of the Exchange volumes.
As a best practice, I typically configure any VMFS datastore volume with vCenter synchronized snapshots. You can probably get away with no-synchronization for a VMFS datastore volume with OS drives but I like knowing that with vCenter sync'd snapshots that I'm getting a mountable RPO that is VMware consistent.
Hope this helps.
Bryan Rogers wrote:
My question is should I snapshot the db, logs and os disks at the same time?
Also - do I need to use any synchronization when snap shotting a Windows OS vmdk that has Exchange installed bearing in mind that the logs and databases are in a different collections and use synchronization.
The answer to both is no. You do not need or want the os in the same collection as the db and logs.