proxmox zfs with VM ext4 disks fstab

[workpush]

Hello everyone,

I'm currently running a proxmox ve 8 environment with ZFS for my pve and my data volumes.
My machine has plenty of RAM for my guests but for data just HDDs. So I added a mirrored SSD pool to use as L2ARC and ZIL.

As VMs I mainly use Debian-based machines with ext4 formatted disks. I don't have SWAP configured.
From Proxmox perspective they are in "write-back" mode.

I was wondering about the best disk/mount options on these disks to benefit from the ZFS caching mechanisms for writing and reading.

1. Is "write-back" on ZFS a good choice? I found several opinions. Some say yes, others say no. What do you think?
2. On my machines(Debian 11 & Debian 12) I mainly use the following fstab config to mount my disks
```
UUID="ABC" /mnt/personal ext4 defaults,user_xattr 0 0
```
Should I use there an additional e.g. "no-cache" argument?

Maybe you can tell me, how you did your configuration?

Thank you!!

 

[Dunuin]

So I added a mirrored SSD pool to use as L2ARC and ZIL.

That usually won't help much to speed up HDDs unless you got specific workloads that can benefit from that (which most people don't).
Would be better to use them as special devices or even as a dedicated pool to store the virtual disks of VMs that need the IOPS.

I was wondering about the best disk/mount options on these disks to benefit from the ZFS caching mechanisms for writing and reading.

1. Is "write-back" on ZFS a good choice? I found several opinions. Some say yes, others say no. What do you think?
2. On my machines(Debian 11 & Debian 12) I mainly use the following fstab config to mount my disks

"cache=none" is the default and recommended for ZFS. Your guestOSs are already caching in RAM. ZFS is caching the same data in RAM. No need to cache the same data a third time in RAM by using "writeback".