Guide · Storage models

RAID vs unRAID

Traditional RAID and ZFS stripe data across every disk in the array. unRAID instead writes whole files to individual disks and protects them with one or two dedicated parity disks. That single design choice drives every practical difference.

Capacity and mixing drives

Striped RAID and RAIDZ want matched disks; the array sizes to the smallest one. unRAID lets you mix any sizes and grow one disk at a time, as long as a parity disk is at least as large as your biggest data disk.

Performance

Striped RAID and RAIDZ read and write across all disks, so throughput scales. unRAID reads at single-disk speed and writes slower still because each write also updates parity. For a media server that is usually fine; for databases or heavy IO it is not.

Failure behavior

If failures exceed parity, striped RAID and RAIDZ can lose the whole array. unRAID is more graceful: lose more disks than parity and you only lose the data on the failed disks, since each disk holds complete files. That containment is unRAID's signature advantage.

Which to choose

Pick unRAID for a mixed-drive, power-efficient media and file server. Pick ZFS/RAIDZ for performance, checksumming, and snapshots. Model either one in the storage calculator, or read how RAIDZ works.