Issues with Fractional Reserve on NetApp FAS8020

FlorianArg — Wed, 04 Jun 2025 13:49:06 GMT

Hi,

Here some info :

- NAS NetApp FAS8020

- Cluster mde 8.2.2

- Volume used for VmWare Datastore and created with the Provision Storage for VmWare utility

- Options used for the volumes : no snapshot - dedup on - fractional reserve 100%

- Vm created with disk provisioned immediately ( so not thin )

We encounter some issues or strange comportments on our volumes and after few investigations, we find out that it come from the fractional reserve parameter à 100% by default on the volumes

The fact are :

- When we created a VM ( Linux or Windows) , the datastore take 100% of the VM size so it seems that the fractional reserve is not used in that case

- When we migrate a Linux VM from a datastore A to a datastore B, we need to have a datastore B with 200% VM size during the opération and after the operation, the datastore B keep 200% of the VM size --> Is it a normal comportment ? ( we undestrand that il come from the fractional reserve because, if we unchecked the fractional reserve, the datastore take 100% of the VM size)

- When we migratd a Windows VM from a datastore A to a datastore B, we need to have a datastore B with 200% VM size during the opération and after the operation, the datastore B do not keep 200% of the VM size but only 140-150 % and not always the same values --> Is it a normal comportment and why it is different than a Linux VM? My guess is that the dedup is working on the volume so that's why the datastore do not keep 200% of eack Windows VM but i'm not sure of that

A last question : I was not able to find the correct best practice for the fractional reserve, do we have to use it for VMWare datastore if we don't use snapshot and disk immediately provisioned ?

Thanks a lot for your help or advices and sorry for my English in advance !

Florian

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Issues with Fractional Reserve on NetApp FAS8020