zfs-raid-comparison.md

RAIDZ levels comparison

	ZFS Stripe	ZFS Mirror	RAIDZ1	RAIDZ2	RAIDZ3	ZFS Stripe of mirrors
Min number of disks	1	2	2	4	5	4
Fault to­le­ran­ce	None	(N-1) disk	1 disk	2 disks	3 disks	(N-1) disk in each N-disk mirror
Disk space over­head	None	(N-1)/N	1 disk	2 disks	3 disks	(N-1)*P for P stipe over N-disk mirrors
Usable Storage	~97%	~50%	~64%	~47%	~38%	~49%
Read speed	Very fast	Fast	Slow	Slow	Slow	Fast
Write speed	Very fast	Fair	Slow	Slow	Slow	Fair
Hard­ware cost	Cheap	High to highest	High	Very high	Very High (disks)	High to highest
Summary	Unreliable storage of relatively large capacity	Reliable storage of relatively small capacity	Large, reliable, relatively expensive but slow storage	Large, highly reliable, relatively expensive but slow storage	Large, highly reliable, relatively expensive but slow storage	Large, fast, reliable, but expensive storage

ZFS Stripe

Sharing of data between disks in ZFS Stripe looks like:

Disk 1	Disk 2
1	2
3	4
5	6

ZFS Mirror

Disk 1	Disk 2
1	2
3	1
2	3

RAIDZ

Disk 1	Disk 2	Disk 3
A1	A2	Ap
B1	B2	Bp
C1	C2	Cp

RAIDZ2

Disk 1	Disk 2	Disk 3	Disk 4
A1	A2	Ap	Ap
Bp	B2	Bp	B1
C1	Cp	Cp	C2

RAIDZ3

Disk 1	Disk 2	Disk 3	Disk 4	Disk 5
A1	A2	Ap	Ap	Ap
Bp	B2	Bp	B1	Bp
C1	Cp	Cp	Cp	C2

ZFS Stripe of mirrors

Disk 1	Disk 2	Disk 3	Disk 4
A1	A1	A2	A2
A3	A3	A4	A4
A5	A5	A6	A6