RAID Capacity Calculator
Usable space, storage efficiency and how many disks can fail for RAID 0, 1, 5, 6 and 10, with the capacity your computer will actually report.
Results
What this tool does
Disk makers count a terabyte as 10¹² bytes but most operating systems divide by 2⁴⁰, so a 4 TB disk shows up as about 3.64 'TB' — the second result gives that figure. RAID 5 survives one failed disk and RAID 6 two; RAID 10 is guaranteed to survive one and may survive one per mirror pair. With today's large disks, rebuilding a RAID 5 takes many hours under heavy load, which is why RAID 6 is often preferred for big arrays. RAID is not a backup: deleted or encrypted files are deleted or encrypted on every disk at once.
Formula
RAID 0: n × s · RAID 1: s · RAID 5: (n − 1) s · RAID 6: (n − 2) s · RAID 10: n ÷ 2 × s
Variables
| Symbol | Meaning | Unit |
|---|---|---|
nd | Number of disks | — |
ds | Size of each disk | TB |
lv | RAID level | — |
U | Usable capacity | TB |
UT | Usable capacity as the operating system shows it | TiB |
EF | Storage efficiency | % |
FT | Disks that can fail without data loss (guaranteed) | — |
OK | Is this a valid setup? | — |
Worked example
- Number of disks4
- Size of each disk4 TB
- RAID level5
- Usable capacity12.00 TB
- Usable capacity as the operating system shows it10.91 TiB
- Storage efficiency75.0 %
- Disks that can fail without data loss (guaranteed)1
- Is this a valid setup?Yes
Limitations
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.