zfs will use half of memory by default for his buffer cache. (and linux kernel can't retreive it like classic linux buffer memory)The short story:
In proxmox 6 fallocate: fallocate failed: Operation not supported
The long story:
Sometimes I can't start my virtual machine because Proxmox says that there is not enough memory space (and it is very strange because I have a server with 16GB of RAM and my KVM is configured to use only 8GB) .
I installed Proxmox v6 in raid-0 zfs and noticed that no swap file was created (and it is very very strange!).
I thought of creating one in the hope of solving the problem but I encountered another error: it is not possible to use the "fallocate" command.
To reproduce the problem of not starting the KVM it is sufficient to do so:
- launch Proxmox;
- make a copy from one server to another with the "scp" command of a backup file of the kvm of at least 10 GB file;
- restore the kvm on the server in use;
- start the kvm and you'll meet the error;