RAID 6+0, usually written RAID 60, stripes data across two or more RAID 6 groups. Each group keeps its own double parity, so it can survive two drive failures on its own. The outer RAID 0 stripe spreads reads and writes across those groups but adds no redundancy of its own. If one entire RAID 6 group is lost, the whole striped volume is lost.
How the layout works
The name describes two layers. The “6” is the inner layer: each RAID 6 group stores parity that is equivalent to two drives, so any two drives in that group can fail without data loss. The “0” is the outer layer: data is striped across the groups, the same way RAID 0 stripes across disks. Seagate describes RAID 60 as RAID 0 striping with RAID 6 double parity across multiple RAID 6 groups, in its RAID Manager User Manual on RAID levels. Dell uses the word “span” for the same idea and describes RAID 60 as striping over more than one span of physical disks configured as RAID 6, in its iDRAC9 User’s Guide entry for RAID level 60.
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Because the parity lives inside each group, the outer stripe never has to hold redundancy. That is what separates RAID 60 from a single large RAID 6 array: the protection is attached to the groups, not to the volume as a whole.
How many drives RAID 60 needs
Seagate states that RAID 60 requires a minimum of eight drives in its implementation. Dell’s example uses four physical disks per RAID 6 group, with a second group of four, which gives the same eight-drive total. Treat eight as the documented floor for these vendors, not a universal rule. Controllers and software stacks set their own limits on span size and total drive count, so check the limits for your specific hardware before you buy drives.
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Usable capacity
For groups of equal size, Dell gives the nominal capacity as s × (n − 2), where s is the number of spans and n is the number of drives in each span. The subtraction of two drives per span is the RAID 6 parity cost. The result is counted in drive-equivalents, meaning multiples of one member drive’s capacity, and it excludes formatting and other controller overhead.
| Spans (s) | Drives per span (n) | Total drives | Nominal capacity (drive-equivalents), s × (n − 2) |
|---|---|---|---|
| 2 | 4 | 8 | 4 |
| 2 | 8 | 16 | 12 |
| 3 | 4 | 12 | 6 |
| 4 | 6 | 24 | 16 |
Two eight-drive groups therefore give 12 drive-equivalents of nominal capacity from 16 drives, which is 75 percent efficiency before overhead. The Seagate and Dell pages cited here do not state a publication date for these figures, so confirm them against the manual version for your controller.
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Fault tolerance: judged group by group
Each RAID 6 group tolerates two failed drives. Tolerance is not pooled across the whole volume, so the outcome depends on where the failures land:
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- One failed drive in each of several groups: every group stays online, and the volume remains available.
- Two failed drives in one group: that group runs degraded but still holds its data, and the volume remains available.
- Three failed drives in one group: that group exceeds its double-parity protection even if every other group is healthy, and because RAID 0 has no redundancy, the striped volume becomes unavailable.
The Linux kernel’s device-mapper RAID documentation is a useful reference for how RAID 6 parity behaves at the group level. The practical lesson is to think of each group as its own failure domain. Failures spread across groups are far less dangerous than the same number concentrated in one.
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Performance: what the vendors actually claim
Seagate characterizes RAID 60 as offering improved performance compared with RAID 6. Dell lists better read performance and slower write performance. Neither source gives benchmark figures, workload definitions or test conditions, so no numerical speed advantage can be attributed to RAID 60 from these pages. Because the outer stripe spreads I/O across groups, read-heavy workloads are the most likely to benefit; write-heavy workloads should be tested on the actual platform before you assume any gain.
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Seagate’s manual warns that initialization and rebuild operations take longer on its RAID 60 implementation than on standard RAID levels. Large drives make this matter more: a longer rebuild is a longer window in which a further failure in the same group can cause loss.
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RAID is not a backup. A RAID 60 array protects against drive failure, not deletion, corruption, ransomware or a failed controller. Seagate advises backing up important files before making any change to an existing array, as covered in its RAID Manager manual on concepts and terminology.
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- Confirm the controller or platform supports RAID 60 and check its minimum and maximum drive counts per span.
- Calculate nominal capacity with s × (n − 2) and subtract formatting and hot-spare overhead.
- Decide whether the failure-domain layout is acceptable: a three-drive failure inside one group is fatal to the volume.
- Benchmark your own read and write mix, because the vendor statements are qualitative.
- Plan rebuild time for your drive size and keep an independent, tested backup of important data.
RAID 60 is a sound choice when you need more capacity and parallel I/O than a single RAID 6 group offers, and you accept that each group is its own point of failure.
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