What could cause VM disks, that are on NFS datastores, to automatically change from Thin to Thick?

[pasalott]

We are currently running vSphere 6.7 U3.  We've noticed than on an increasing number of VMs, disk type is changing from Thin to EagerZeroedThick.  VMs with multiple disks may just have one or a few of the disks that change to EagerZeroedThick, while the others remain Thin.  These disks are on NFS datastores.  Our hosts in the DMZ uses fiber channel storage formatted with VMFS 6.  The issue does not appear to be happening on these volumes.  What could cause the disk type to automatically change from Thin to EagerZeroedThick (other than a storage vMotion, which isn't the cause here)?

Also, when attempting to change the disk back to Thin, via a storage vMotion to a different datastore, most of the time the disk remains EagerZeroedThick and unable to change.

I'm still hunting logs for clues and running reports daily to find VMs where disks recently changed to Thick so we can pinpoint any useful information in the event logs.

[nachogonzalez]

What is the default storage policy that you are using?

[Lalegre]

Hello @pasalott,

May I know from which vendor is the NFS that you are using?

[pasalott]

Looks like Datastore Default is the policy.  The vendor is NetApp

[pasalott]

Something else that is odd.  For all the VMs that I have checked, using NFS (NetApp) storage, there is no option to change disk type when performing a storage vmotion (whether powered on of off).  Disk type has Thin Provision listed and greyed out with no option to select a different type.  There are no storage policies applied (just datastore default).  For any VM not using NFS (NetApp) storage, the option to change disk type is available.

[lucasbernadsky]

Hi there! Considering your replies to Nacho and Leandro, I would suggest opening a SR to NetApp. It seems to be a known issue here: https://kb.netapp.com/Advice_and_Troubleshooting/Data_Storage_Software/NetApp_NFS_Plug-in_for_VMware...

If you try to storage vMotion a VM from Netapp datastores to non-netapp ones, can you change disk type on the fly?

[nachogonzalez]

Agree with this!

[pasalott]

Thanks.  I looked into it with our storage team.  NetApp volumes are all set to thin disk, which is probably why we only have Thin Disk as an option on the VMware side.  Now it seems to be a matter of running vCheck reports daily to see if any new VMs appear with thick disks, so we can pinpoint any information in the event logs.  Just not sure what would cause a VM disk to automatically change from thin to thick on it's own without performing a storage vmotion.  Our list of VMs with thick disks are growing and these are not new VMs.  This issue could become critical since we are oversubscribed on the Netapp side and will quickly run out of space if thin disks continue to automatically convert to thick.

[MiguelAraujo]

thanks for the info

[Lalegre]

Hey @pasalott,

Regarding to what @lucasbernadsky pointed to you, are the storage team presenting the datastore over the LIFs?

[Ewing1]

https://kb.vmware.com/s/article/68107