RAID Calculator
RAID capacity calculator for RAID 0, 1, 5, 6, 10, 50, 60, JBOD and ZFS RAIDZ: usable space, efficiency, drive failures tolerated and speed, in TB or TiB.
RAID is not a backup: deletion, ransomware and controller faults affect every drive at once.
| Level | Usable | Efficiency | Failures tolerated / why not |
|---|---|---|---|
| RAID 0 | 16 | 100% | 0 |
| RAID 1 | 4 | 25% | 3 |
| RAID 5 | 12 | 75% | 1 |
| RAID 6 | 8 | 50% | 2 |
| RAID 10 | 8 | 50% | 1 |
| RAID 50 | — | — | RAID 50 with 2 groups needs a multiple of 2 drives and at least 3 per group (6+). |
| RAID 60 | — | — | RAID 60 with 2 groups needs a multiple of 2 drives and at least 4 per group (8+). |
| JBOD | 16 | 100% | 0 |
| RAIDZ1 | 12 | 75% | 1 |
| RAIDZ2 | 8 | 50% | 2 |
| RAIDZ3 | — | — | RAIDZ3 needs at least 5 drives. |
Every RAID level trades capacity for safety and speed. This calculator shows how much space you really get from a set of drives in RAID 0, 1, 5, 6, 10, 50, 60, JBOD or ZFS RAIDZ1–3, how many drives can fail without losing data, and the relative read speed and write penalty. Mixed drive sizes are handled with the smallest-drive rule, and a table compares every level for the same drives.
How to use this tool
- Pick the RAID level.
- Enter the number of drives and their size — or list mixed sizes, one per line.
- For RAID 50 or 60 set the number of span groups.
- Choose TB or TiB and compare the levels in the table.
Formula
RAID 0 = n·s · RAID 1 = s · RAID 5 = (n − 1)·s · RAID 6 = (n − 2)·s · RAID 10 = n/2·s · RAID 50 = (n − g)·s · RAID 60 = (n − 2g)·s · RAIDZp = (n − p)·s
n is the number of drives, s the size of the smallest drive and g the number of span groups. The write penalty is the number of disk I/Os one random write costs (2 for mirrors, 4 for single parity, 6 for double parity). 1 TB = 10¹² bytes; 1 TiB = 2⁴⁰ bytes, so 1 TB ≈ 0.909 TiB.
Example
Four 4 TB drives give 16 TB raw. RAID 5 keeps (4 − 1) × 4 = 12 TB (75%) and survives one failure; RAID 6 and RAID 10 both keep 8 TB (50%) — RAID 6 survives any two failures, RAID 10 is faster for writes. Your operating system will show the 12 TB as about 10.91 TiB.
Frequently asked questions
RAID 5 or RAID 6?
With large drives, RAID 6. Rebuilding a failed multi-terabyte drive can take a day or more, and RAID 5 has no protection left during that time.
Why does my NAS show less than this?
Operating systems count in binary units (TiB) and file systems reserve space for metadata and snapshots. Choose TiB above to see the binary figure.
Can I mix drive sizes?
Standard RAID uses only as much of each drive as the smallest one provides. Synology SHR, Unraid or a JBOD use the extra space, at the cost of different protection rules.
Is RAID a backup?
No. It protects against drive failure, not against deletion, ransomware, fire or a failing controller. Keep a separate backup.
Last updated:
Page address with these inputs: https://kakao.mobile/tools/raid-calculator/
Cite or embed this tool
kakaoCalc. (2026, November 8). RAID Calculator. https://kakao.mobile/tools/raid-calculator/
“RAID Calculator.” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/raid-calculator/.
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