ZFS share

[mieszkobiedak]

Hi,

I'm trying to mount ZFS pool, called it 'giant' (consists of 3x 12TB hdd) with the existing VM which runs OpenMediaVault, can't assign whole available space to the hard drive.

Hardware
Hingle mobo, standalone proxmox installation on nvme which means I have 1 proxmox node i my datacenter and those 3 HDDs attached to SATA configured as zfs pool in that single proxmox node. Here's what I've done:

Problem
1. Attached drives to mobo
2. Configured ZFS Raidz1 pool (total 36TB, raidz1 should give me about 24TB to use)
3. Created ZFS in Storage section
4. Tried to create a 23TB hard drive for OMV VM -> it fails with errors no space left if I want to use whole space from ZFS ~23TB. The most I was able to go to was 16TB.

Questions I am not able to answer:
1. Why I cannot use all space from ZFS in a single Hard Drive ?
2. What is the proper way to use ZFS pool by VMs in proxmox ?

I have read a great deal of tutorials, documentation and watched some youtube videos, however this still puzzles me. Counting on you wisdom...

 

[Neobin]

https://forum.proxmox.com/threads/can-not-add-hard-disk-out-of-space-500.118150/#post-511599

 

[mieszkobiedak]

Thank you for sharing this Neobin.

Although it was still not enough information, that answer suggests it's something called "padding overhead", no confirmation, no digging.

It seems that with ZFS in RaidZ you will lose space not only to the data parity but also to storage overhead (another 20% !), which I was not aware of.

For those actually interested in finding out why that space is not available for use and how to verify it I have found out more here.

By quickly reading that article it seems there is much configuration that can be done with ZFS, so it can be adjusted to its purpose which I find very useful. Also running ZFS blindly is going to work but you have to expect to cost you more space, cpu, ram etc.

Lots of useful info about ZFS can be found in Truenas docs like this one - https://www.truenas.com/docs/references/zfsdeduplication/