RAID Calculator Widget
Storage vendors, homelab blogs and IT teams can let readers size an array: choose the RAID level, the number of drives, their size and (for RAID 50/60) the span groups, and see usable capacity, efficiency, how many drive failures the array survives and what a 1,024-based OS will report.
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<iframe src="https://a2z.tools/embed/w/raid-calculator" title="RAID Calculator by A2Z Tools" width="100%" height="560" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>
A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.
<div data-a2z-widget="raid-calculator" data-height="560"></div> <script async src="https://a2z.tools/embed.js"></script>
Adds a small script (what it does) that sizes the widget to fit its content, loads it lazily and keeps it isolated from your page's CSS.
Works with
How it works
RAID - redundant arrays of inexpensive disks, named in the 1987 Berkeley paper by Patterson, Gibson and Katz - trades capacity for redundancy. With n equal drives of size s, striping (RAID 0) uses all n x s and survives no failure; mirroring (RAID 1) keeps one drive's worth however many copies there are; single parity (RAID 5) gives (n - 1) x s and survives one failure; double parity (RAID 6) gives (n - 2) x s and survives two; RAID 10 mirrors pairs and stripes them, keeping half. RAID 50 and 60 stripe across g parity groups, losing one or two drives per group. The widget enforces minimums - 3 drives for RAID 5, 4 for RAID 6 and RAID 10, an even count for RAID 10, and equal groups of at least 3 or 4 for 50 and 60 - and states the rule when it refuses. Four 4 TB drives in RAID 5 give 12 TB (10.91 TiB) at 75% efficiency. It covers capacity only.
Calculation method
- RAID 0: n x s (n >= 2), 0 failures; RAID 1: s (n >= 2), n - 1 failures
- RAID 5: (n - 1) x s (n >= 3), 1 failure; RAID 6: (n - 2) x s (n >= 4), 2 failures
- RAID 10: n / 2 x s (even n >= 4), 1 guaranteed, up to n / 2 if each failure is in a different mirror
- RAID 50: (n - g) x s, g groups of >= 3; RAID 60: (n - 2g) x s, g groups of >= 4; n divisible by g
- Efficiency = usable / raw; TiB = TB x 10^12 / 2^40
Worked examples
Small NAS
Inputs: RAID 5; 4 drives x 4 TB
Result: 12 TB usable (10.91 TiB); 75% efficiency; survives 1 failure
One drive's worth goes to parity.
Striped double parity
Inputs: RAID 60; 8 drives x 8 TB; 2 groups
Result: 32 TB usable (29.1 TiB); 50% efficiency; 2 failures guaranteed, up to 4
Each group of four loses two drives to parity.
Limitations
- Capacity and fault tolerance only - no performance, rebuild time or failure-probability estimates.
- Assumes identical drives and ignores hot spares, controller metadata and file-system overhead.
- Vendor-specific layouts (RAID-Z, SHR, unRAID) differ and are not modelled.
Where publishers use it
- A NAS manufacturer's buying guide comparing RAID 5 and RAID 6
- A homelab blog planning a new storage server
- A server reseller's configurator help page
- An IT certification course on storage fundamentals
- A video-production studio's page on safe shared storage
Questions
How much space do I get from four 4 TB drives in RAID 5?
(4 - 1) x 4 TB = 12 TB, a storage efficiency of 75%. An operating system counting in powers of 1,024 shows it as about 10.91 TiB, before file-system overhead.
RAID 6 or RAID 10?
With six 8 TB drives, RAID 6 gives 32 TB and survives any two failures; RAID 10 gives 24 TB and is guaranteed to survive only one (more if the failures hit different mirror pairs). RAID 6 stores more and tolerates any two failures; this widget does not compare speed.
Why does RAID 10 need an even number of drives?
RAID 10 is a stripe of mirrored pairs, so every drive needs a partner. With five drives one would be left over; most controllers either refuse or leave it as a hot spare.
What are span groups in RAID 50 and 60?
The drives are split into equal groups, each a RAID 5 (or RAID 6) set, and data is striped across the groups. Eight drives in two RAID 6 groups lose four drives to parity and keep 4 x size - but can survive up to four failures if they are spread across the groups.
Can I mix drive sizes?
Most hardware and software RAID treats every member as the size of the smallest drive, so mixing a 4 TB and an 8 TB drive wastes 4 TB. The widget assumes equal drives.
Is RAID a backup?
No. RAID keeps an array running through drive failures, but deletions, ransomware, file-system corruption and controller faults affect all copies at once. Keep separate backups.
Sources
- A Case for Redundant Arrays of Inexpensive Disks (RAID) - Patterson, Gibson and Katz, UCB/CSD-87-391 - University of California, Berkeley EECS . The technical report that defined RAID levels with mirroring and parity; levels 0, 6, 10, 50 and 60 are later industry conventions built on the same ideas. Checked 2026-10-01.
Cite or recommend this tool
If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.
A2Z Tools RAID Calculator https://a2z.tools/embed/raid-calculator
<a href="https://a2z.tools/embed/raid-calculator">A2Z Tools RAID Calculator</a>
[A2Z Tools RAID Calculator](https://a2z.tools/embed/raid-calculator)
RAID Calculator by A2Z Tools - https://a2z.tools/embed/raid-calculator
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