vSphere 7 Update 1 & vSphere Clustering Service (vCLS)

  • 2 February 2021
  • 2 replies

Userlevel 3
Badge +6

vCenter 7.0U1c and vSphere Clustering Service VMs on local or shared storage.

After test upgrading vCenter from 6.5U3 to 7.0U1c (which worked just fine w 0 issues), every vmware cluster with DRS and/or HA enabled gets 3 new vCLS (very tiny VMs w 2GB storage/.13GB RAM).

When NCC is ran it registers 3 WARNs that there are VMs running on the SATADOM’s. I would assume that, even what (little) they do (today), would this wear out Satadom’s or M.2’s?

Would this be a concern for G4/G5’s (w Satadoms) and not G6/G7’s (M.2’s)?”

While vCLS can be moved to shared storage, wouldn’t they be moved back to local storage during an NX cluster stop?

(Like to point out this was done in a LAB environment, not in Production… no bits nor bytes were harmed during the upgrade progress.)

2 replies

Userlevel 6
Badge +5

Hi DavidN,

Not evading the rest of your questions (still checking) but to address some of what you are asking, it seems that vCLS is placed on the local storage as the last resort option

Datastore selection for vCLS VMs

The datastore for vCLS VMs is automatically selected based on ranking all the datastores connected to the hosts inside the cluster. A datastore is more likely to be selected if there are hosts in the cluster with free reserved DRS slots connected to the datastore. The algorithm tries to place vCLS VMs in a shared datastore if possible before selecting a local datastore. A datastore with more free space is preferred and the algorithm tries not to place more than one vCLS VM on the same datastore. You can only change the datastore of vCLS VMs after they are deployed and powered on.




If no shared storage is available, the agent VMs are placed on local storage. If a cluster is formed before shared storage is configured on the ESXi hosts, as would be the case when using vSAN, it is strongly recommended to move the vCLS agent VMs to shared storage after.


In terms of wearing off local storage, I would address that question to VMware as they are more equipped to answer it. They designed it after all.

As for the migration of the vCLS back to the local storage during the cluster stop, wouldn’t you power them off first and then stop the cluster?

Userlevel 3
Badge +6

If a vCLS VM is powered off, it’s powered back on immediately; if one is somehow deleted, a new one is brought up to replace it (so there would be 3 on any vmware Cluster of hosts).

So, only storage vMotion is an option - which depending on license type may not be available to everyone.

In any case, we successfully rolled back to the previous vCenter (followed supported process and all came back ok.) Probably going to wait a while until some of these questions are resolved. For now we’re going w latest 6.7… vCLS can be powered off/removed afterwards without any issues.