Free study tool
RAID capacity calculator
Pick a RAID level, a number of drives, and a drive size to see the usable capacity, the efficiency, and how many drive failures the array survives.
Useful for CompTIA A+ Core 1
Your array
6,000 GB usable.
- Usable capacity
- 6,000 GB
- Raw capacity
- 8,000 GB
- Efficiency
- 3/4 (75%)
- Drive failures survived
- 1
Worked steps
- 14 drives of 2,000 GB give 8,000 GB of raw space.
- 2RAID 5 needs at least 3 drives, and you have 4.
- 3RAID 5 spends one drive's worth on parity: 4 − 1 = 3 drives of data.
- 43 × 2,000 GB = 6,000 GB usable.
- 5Single parity means the array survives any one drive failure.
- 6Efficiency is 6,000 GB of 8,000 GB, or 3/4 (75%).
Sources
- Defining RAID Volumes for Intel Rapid Storage Technology
Intel · RAID 5 needs at least three drives, gives the smallest drive's size times one less than the drive count, and survives one drive failure.
- md(4): Linux software RAID
man7.org · RAID levels 4 and 5 survive the failure of one device.
RAID levels at a glance
| Level | Minimum drives | Usable space | Failures survived |
|---|---|---|---|
| RAID 0 | 2 | All drives (n) | None |
| RAID 1 | 2 | One drive | All but one |
| RAID 5 | 3 | n − 1 drives | One |
| RAID 6 | 4 | n − 2 drives | Two |
| RAID 10 | 4, even | n ÷ 2 drives | One for sure; one per mirror pair at best |
The calculator assumes every drive is the same size. With mixed sizes, most implementations treat every drive as the size of the smallest one.
Drive makers count a gigabyte as 1,000,000,000 bytes, while many operating systems report capacity in binary units. A 2,000 GB drive shows up as about 1,863 GiB, which is the same space measured differently.
Common questions
- Is RAID a backup?
- No. RAID keeps an array running through a drive failure, but deleted files, ransomware, and corruption are copied to every drive at once. Backups still need to be separate copies.
- How much space do I get from four 2 TB drives in RAID 5?
- 6 TB. RAID 5 spends one drive's worth of space on parity, so four drives give three drives of usable space, and the array survives one drive failure.
- What is the difference between RAID 5 and RAID 6?
- RAID 6 stores a second set of parity, so it needs at least four drives and gives up two drives' worth of space, but it survives any two drive failures instead of one.
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