Size printed on the drive label. Different sizes? The array uses the smallest one for every drive.
Advanced settings
Typical hard drive: 100–200 MB/s with no other load. SSD: 400 MB/s or more.
From the drive datasheet. It is a worst-case spec, so real drives usually do better.
Drives that can fail
Rebuild of one drive
Read error during rebuild
Checks for this setup
The same drives in every RAID level
12 drives of 16 TB each.
RAID 60 at a glance
| Minimum drives | 8 |
|---|---|
| Usable space | (drives − 2 × number of groups) × size of the smallest drive |
| Drives that can fail | 2 per group |
| Read speed | High |
| Write speed | Better than one large RAID 6 |
| Rebuild | Reads only the affected group, still protected |
How RAID 60 works
The drives are split into spans, each one a RAID 6, and data is striped across the spans. This calculator uses two spans of equal size. Each span gives up two drives to parity.
Why use RAID 60 instead of one big RAID 6?
A single RAID 6 of 20 or 24 large drives reads a huge amount of data in every rebuild, and every drive takes part. Splitting it into two RAID 6 spans halves the data read per rebuild, keeps the other span at full speed and allows up to two failures in each span. The cost is two more drives of parity.
When RAID 60 is used
Large file servers, backup targets and video archives with 12 to 24 or more drives, usually on hardware controllers. With ZFS, the equivalent is a pool of several RAIDZ2 groups.
Questions
What is the minimum number of drives for RAID 60?
Eight: two RAID 6 groups of four drives.
How many drives can fail in RAID 60?
Any two in each group, so up to four if they are spread evenly.
RAID 60 or RAID 6?
Up to about 12 drives, one RAID 6 is simpler and gives more space. Above that, RAID 60 keeps rebuilds shorter.