ZFS Overview: The Last Word in Filesystems

What is ZFS?

ZFS (Zettabyte File System) is a combined filesystem and volume manager originally developed by Sun Microsystems. It provides:

• Data integrity - End-to-end checksums detect corruption
• Pooled storage - Combine multiple disks into a single pool
• Snapshots - Instant point-in-time copies
• Compression - Transparent compression
• RAID - Built-in software RAID (RAID-Z1, Z2, Z3)
• Deduplication - Optional block-level dedup
• Copy-on-write - No risk of partial writes

Key Concepts

Pools (zpools)

The foundation of ZFS storage. A pool combines one or more virtual devices (vdevs) into a single storage unit.

# View pools
zpool list

# Pool status with disk info
zpool status

# Example output:
#   pool: zroot
#  state: ONLINE
# config:
#         NAME        STATE     READ WRITE CKSUM
#         zroot       ONLINE       0     0     0
#           da0p3     ONLINE       0     0     0

Datasets

ZFS filesystems within a pool. Each dataset can have its own properties (compression, quota, etc.).

# List datasets
zfs list

# Example output:
# NAME                   USED  AVAIL  REFER  MOUNTPOINT
# zroot                 10.5G  89.5G    96K  /zroot
# zroot/ROOT             5.2G  89.5G    96K  none
# zroot/ROOT/default     5.2G  89.5G  5.2G  /
# zroot/home             2.1G  89.5G  2.1G  /home

Snapshots

Read-only point-in-time copies of a dataset. Snapshots are nearly instant and space-efficient.

# Create snapshot
zfs snapshot zroot/home@backup-2025-01-15

# List snapshots
zfs list -t snapshot

# Rollback to snapshot
zfs rollback zroot/home@backup-2025-01-15

RAID-Z Levels

Common Properties

# Enable compression (lz4 recommended)
zfs set compression=lz4 zroot/home

# Set quota
zfs set quota=50G zroot/home/user

# Enable access time recording
zfs set atime=off zroot  # Improves performance

# Check compression ratio
zfs get compressratio zroot/home

Why ZFS on FreeBSD?

FreeBSD has first-class ZFS support:

• Native kernel module (not FUSE)
• Boot from ZFS
• Root-on-ZFS with boot environments
• Well-tested and production-ready
• OpenZFS project keeps it current