ZFS Commands

Introduction

There are lots of commands that will show and control how the ZFS pools are run on the Proxmox hosts so we need a brief guide to ZFS

What is ZFS

To understand ZFS at a technical level, you must treat it as a combined file system and logical volume manager. This integration allows the file system to be aware of the underlying disk structure, which is the core of its data integrity features.

Physical Disks (vdev members)

The base layer consists of block devices (e.g., /dev/nvme0n1). ZFS uses Copy-on-Write (CoW) at this level. When data is modified, ZFS writes the new data to a new block and then updates the pointers, rather than overwriting the old data. This prevents data corruption during power loss.

A VDEV (Virtual Device) is the mathematical arrangement of physical disks.

• Mirror: Data is written to n disks. Read IOPS scale with the number of disks; write IOPS match a single disk.
• RAID-Z1: Distributes data and a single parity stripe across n+1 disks. It provides n disks of capacity eg 3 16Tb HDs as Z1 will give ((3-1) x 16)32TB usable capacity or 4 x 16TB would give ((4-1) x 16) 48TB.
• VDEV Failure: If a VDEV loses its redundancy (e.g., two disks fail in a RAID-Z1), the entire ZPool is lost because ZFS stripes data across all VDEVs in a pool (RAID 0 across VDEVs).