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Full Name: Burak

Is ReFS for Hyper-V 2016 Host safe?

Post by burak » Mar 22, 2017 12:51 am


we are planning to build two new server with Server 2016 as Hyper-V host and using Veeam 9.5.
There is no SAN storage just those two servers which are holding the VM files. We want to use ReFS for the partitions which stores the VM files.

It seems that there are some problems with ReFS, huge data sizes and 4k cluster size (and sometimes 64k cluster size) in those threads:
veeam-backup-replication-f2/refs-4k-hor ... 9-150.html
veeam-backup-replication-f2/9-5-refs-se ... 39625.html

Our backup repository is a NAS by using SMB. The NAS itself uses ext4 for the drives. Only the Hyper-V host will be use ReFS.

It is safe to use ReFS for Hyper-V host or can I get any problems like in the threads linked above? It seems that those problems only appear only on ReFS repositories but we won't have that.

Best regards

Mike Resseler
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Full Name: Mike Resseler
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Re: Is ReFS for Hyper-V 2016 Host safe?

Post by Mike Resseler » Mar 22, 2017 6:45 am

Hi Burak,

As far as I know there are no problems when using ReFS and 4k cluster size (recommended by MSFT) for hosting the VM files. In fact, when you are using the new, native backup methods for Hyper-V and VBR 9.5 (don't forget U1) you will see fast checkpoint merges.

However, to be on the safe side, I certainly would recommend to install the latest KB that has been discussed also: ... -kb4015438. See also our KB for more information:


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