Poor performance of VM clones accross volumes

Philipp — Wed, 04 Jun 2025 19:10:55 GMT

Hi,

I'm expiriencing a really poor performance when cloning a virtual machine to another volume/datastore.

First of all my setup:

Scenario:

I have one VM template which is cloned multiple times to different volumes.

Deploying a VM from this template onto the same volume takes less than 5 seconds (as expected)

But deploying the VM to another volume on the same SVM and same aggregate takes about 10 minutes.

Deploying the VM manually using the vSphere client (not cloning from the already deployed template) takes less than one minute (as expected).

So why is the copy process that slow.

I was able to reproduce the problem by copying a vmdk file using vmkfstools via ssh on the esxi host.

Copying the file on the same volume takes less than 5 seconds, but copying the file to another volume also takes about 10 minutes.

VAAI seems to be working properly, because there is nearly no network IO while cloning and vmkfstools (with -v) shows:

VAAI-NAS [vendor_nas_plugin : /vmfs/volumes/af053157-2558df21] : CLONE [/vmfs/volumes/af053157-2558df21/base-6173a53f0ba4f176d00a803f5f6ff38fbf74f97a/test-flat.vmdk] succeeded.

after cloning was successful.

Also sysstat does not show a really high disk utilisation (less than 20%; with other VMs running on the system).

Would be nice if someone can give me some hints on debugging the problem.

Kind regards

Philipp

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