RAID 6 Calculator
RAID 6 stripes data with two drives' worth of parity, so the array survives any two drive failures, including a second failure while it rebuilds from the first.
RAID 6 at a glance
- 11 × 24TB in RAID 6 = 216TB usable (196.45 TiB), 82% of raw capacity; survives 2 drive failures.
- 200TB usable from 24TB drives in RAID 6 takes 11 drives (216TB usable).
Identical drives; decimal TB as drives are sold, binary TiB as most operating systems show it; before filesystem overhead. Hot spares are extra drives and add no capacity.
RAID 6 usable capacity by drive count
| Drives | 1.92TB | 3.84TB | 8TB | 12TB | 16TB | 24TB |
|---|---|---|---|---|---|---|
| 4 | 3.84TB | 7.68TB | 16TB | 24TB | 32TB | 48TB |
| 5 | 5.76TB | 11.52TB | 24TB | 36TB | 48TB | 72TB |
| 6 | 7.68TB | 15.36TB | 32TB | 48TB | 64TB | 96TB |
| 8 | 11.52TB | 23.04TB | 48TB | 72TB | 96TB | 144TB |
| 10 | 15.36TB | 30.72TB | 64TB | 96TB | 128TB | 192TB |
| 12 | 19.2TB | 38.4TB | 80TB | 120TB | 160TB | 240TB |
| 16 | 26.88TB | 53.76TB | 112TB | 168TB | 224TB | 336TB |
Usable capacity in decimal TB, before filesystem overhead. — means the drive count is not valid for RAID 6.
RAID 6 formula
Usable capacity = (n − 2) × S. Minimum 4 drives. Fault tolerance: any 2 drives. Example: 11 × 24TB = 216TB (196.45 TiB); 14 × 24TB = 288TB.
Why RAID 6 for large drives
Rebuilding a large drive means reading every other drive in full. RAID 6 still has one drive of protection during that rebuild, which RAID 5 does not.
Write cost
Each random write costs six disk operations because two parity blocks are updated. RAID 6 suits capacity storage, backups and read-heavy data; for heavy random writes, consider RAID 10.
24TB drives for this array
In-stock 24TB drives from our catalogue, with the price for the 11 drives in the example above. Hot spares are extra.
- Western 0F62798 Western Digital 0F62798 Ultrastar DC HC580 24TB 7200RPM 6Gb/s SATA 512e $960.00 each · 11 drives $10,560.00
- Seagate ST24000NM007H Exos X24 24TB 7200RPM 12Gb/s SAS 512MB Cache 512e 3.5-Inch Hard $1,450.00 each · 11 drives $15,950.00
- Western WUH722424ALE604 Western Digital WUH722424ALE604 Ultrastar DC HC580 24TB 7200RPM $960.00 each · 11 drives $10,560.00
- Dell GPP63 Dell 0GPP63 / GPP63 24TB 7200RPM 12Gb/s SAS 512MB Cache 512e Hot-Pluggable $1,589.47 each · 11 drives $17,484.17
- Western WD240EDGZ Western Digital WD240EDGZ 24TB 7200RPM SATA 6Gb/s 3.5-inch Internal $960.00 each · 11 drives $10,560.00
- 400-BRRZ - Dell 24TB SAS 12Gb/s 7.2K 512e 3.5-inch LFF Brand New Hard Drive for PowerEdge $1,950.00 each · 11 drives $21,450.00
- Seagate ST24000NM000H Exos X24 24TB SATA 6Gb/s 3.5-Inch Hard Drive $987.37 each · 11 drives $10,861.07
- Western 0F62835 Western Digital 0F62835 Ultrastar DC HC580 24TB 7200RPM 12Gb/s SAS 512MB $2,068.42 each · 11 drives $22,752.62
Frequently asked questions
How many 24TB drives do I need for 200TB usable in RAID 6?
11 drives: (11 − 2) × 24TB = 216TB usable (196.45 TiB), before filesystem overhead. Add hot spares on top.
What is the usable capacity of 14 × 24TB drives in RAID 6?
288TB (261.93 TiB): 12 drives of data, 2 of parity.
What is the minimum number of drives for RAID 6?
Four: two of data and two of parity. With four drives, RAID 6 and RAID 10 give the same capacity.
How many drives can fail in RAID 6?
Any two drives, including a second failure during a rebuild.
Does a hot spare change RAID 6 capacity?
No. 200TB from 24TB drives takes 11 drives in RAID 6 either way; with one hot spare you buy 12, and usable capacity stays 216TB.
RAID calculators by level
- RAID calculator (all levels)
- RAID 0 calculator
- RAID 1 calculator
- RAID 5 calculator
- RAID 10 calculator
- RAID 50 calculator
- RAID 60 calculator
RAID planning guides
- How Many Drives Can Fail in Each RAID Level?
- RAID Hot Spare: What It Does and How It Affects Capacity
- TB vs TiB: Why a 24TB Drive Shows 21.8 TiB
- RAID Write Penalty by Level
- Best RAID Level for 2, 3, 4, 5, 6 or 8 Drives
- RAID 50 vs RAID 60
- RAID 6 vs RAID 60
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Updated 2026-10-22.