VMware Solutions Discussions

VSC4.1 Scan Manager question


I ran the scan of one of our datastores using the VSC and noticed as it was doing it it was creating and removing snapshots.

Create virtual machine snapshot

[Netapp] Optimization and Migration deleting snapshots from VM Alignment check

Remove snapshot

Virtual machine disk consolidation succeeded

I watched the utube video on this and read the VSC 4.1 admin guide but didn't see any mention of the actual underlying mechanism of doing the scan.

Whats the reason for the VM snapshot and is this expected?



From page 108 of the 4.1 install and admin PDF

Scanning the datastores

You can use the Optimization and Migration capability to scan VMFS datastores and see which ones are optimized.

About this task

As part of the scan process, the Optimization and Migration capability takes VMware snapshots of the virtual machines that are powered on. As soon as the snapshots are no longer needed, it quickly deletes them to free up that space.


This is briefly described on page 105 of the Virtual Storage Console for VMware vSphere Installation and Administration Guide.

Martin is correct that VSC invokes a vSphere snapshot which is required for powered-on virtual machines on VMFS datastores. This is also why powered-on virtual machines with independent persistent disks on VMFS can't be scanned. (vSphere snapshots can't be created.) vSphere snapshots are also created for VMs on NFS datastores if backed by non-NetApp storage or if the NetApp storage system has not yet been added or discovered under Monitoring and Host Configuration.


Answered my own question:


VSC takes a snapshot of the VMs as the files are locked by the ESX host.

It would be good if this was explained in the docs (I may of missed it of course) as when writing change requests and troubleshooting it's good to know what the underlying mechanism is.

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