The HypestKey RAID calculator shows how much space you actually get from an array after parity and mirroring take their share. Pick RAID 0, 1, 5, 6, 10 or 50, enter the drive count and size, and the raid calculator shows usable capacity, raw capacity, space efficiency, fault tolerance and the minimum number of drives, with a picture of data and parity drives.
Calculating RAID capacity by hand sucks. Nobody wants to sit there with a calculator figuring out how much space they actually get after parity eats some of it. Just use this thing, it is free and works in any browser.
How to use the RAID calculator
- Select the RAID level: RAID 0, 1, 5, 6, 10 or 50.
- Put in your drive count, from 2 to 24. If the level needs more drives, or an even number for RAID 10, the tool corrects the count and tells you.
- Choose the drive capacity from 120 GB to 20 TB, or tap one of the quick sizes from 500 GB to 8 TB.
- Pick whether you want the result in gigabytes or terabytes.
- Read usable capacity, raw capacity, efficiency, fault tolerance and the minimum drives on the right. Right away you see the result, with no button to press.
- Press Copy result to save the numbers for your NAS or server plan.
How this tool works: how does the RAID calculator count usable space?
The HypestKey RAID calculator multiplies the drive size by the number of drives that hold data. For RAID 0 that is all n drives, for RAID 1 one drive, RAID 5 n − 1, RAID 6 n − 2 and RAID 10 half of them. RAID 50 is built as two RAID 5 groups, so four 1 TB drives give 4, 1, 3, 2 and 2 TB, and six drives in RAID 50 give 4 TB.
Efficiency is usable space divided by raw space (all drives added up). Fault tolerance is the number of drives that can fail without data loss: none for RAID 0, all but one for RAID 1, one for RAID 5, two for RAID 6. For RAID 10 it is 1 up to half the drives, because more than one failure is survived only when each one hits a different mirror pair. For RAID 50 it is 1 to 2, one per RAID 5 group.
As on the drive label, 1 TB = 1000 GB. In Windows the count is in binary units, which is why a “1 TB” drive usually shows up as about 931 GB there. The tool assumes all drives have the same size, and with an odd drive count in RAID 50 one drive stays unused, which the verdict points out.
| RAID level | Min drives | Usable space | Drives that can fail | 4 × 1 TB gives |
|---|---|---|---|---|
| RAID 0 | 2 | n × size | 0 | 4 TB (100%) |
| RAID 1 | 2 | 1 × size | n − 1 | 1 TB (25%) |
| RAID 5 | 3 | (n − 1) × size | 1 | 3 TB (75%) |
| RAID 6 | 4 | (n − 2) × size | 2 | 2 TB (50%) |
| RAID 10 | 4, even | n ÷ 2 × size | 1 to n ÷ 2 | 2 TB (50%) |
| RAID 50 | 6 | two RAID 5 groups | 1 to 2 | needs 6 drives |
What are the RAID levels and how do they differ?
There are about 6 common RAID levels, and each trades space, speed and safety differently. In short, RAID 0 gives full space and no protection, RAID 1 mirrors data, RAID 5 loses one drive to parity and survives one failure, RAID 6 loses two and survives two, RAID 10 halves the space for speed, and RAID 50 stripes RAID 5 groups. Here is the short version.
RAID 0
All your drives act as one big fast drive. Buy 4 drives, get 4 drives worth of space. Sounds great until one drive dies. Then you lose everything. Literally everything. Mostly people use it for game libraries, temp files, stuff they can download again. Never put anything important on RAID 0.
RAID 1
Two drives, same data on both. Simple. One dies, the other keeps working. So you are paying for 2 drives but only getting the space of 1. In lots of small business servers the OS runs on RAID 1. It just works.
RAID 5
This is what most people end up using. Minimum 3 drives. Across the drives, parity data gets spread around, so if one drive fails, you do not lose anything. With 4x 1TB drives you get 3TB usable. Good enough for a home NAS, file servers, that kind of thing. Just do not cheap out on the drives.
RAID 6
RAID 5 but paranoid. Two drives can fail at the same time and you are still fine. For that it costs you 2 drives worth of space instead of 1. Makes sense when you have 8+ large drives, because rebuilds take forever and that is when drive #2 likes to fail.
RAID 10
Pairs of mirrors striped together. Four drives minimum, half the space. Fast reads, fast writes. For databases people swear by it, and many database servers run on RAID 10 for exactly that reason.
RAID 50
Enterprise stuff. Multiple RAID 5 arrays striped together. To even start, you need at least 6 drives. Faster rebuilds than one huge RAID 5. Most people will never need this.
Which RAID level should you pick?
For a home NAS with Plex and backups, RAID 5 on four drives is the usual answer. A workstation boot drive does well on RAID 1, a database on RAID 10, a video editing scratch disk on RAID 0, and a two-bay setup on a tight budget on RAID 1. With 8 or more large drives, an array is usually safer on RAID 6.
| Use | Usual pick | Why |
|---|---|---|
| NAS for Plex and backups | RAID 5, four drives | 75% of the space, survives one failure |
| Workstation boot drive | RAID 1 | Simple mirror, keeps working if a drive dies |
| Database | RAID 10 | Fast writes, no parity overhead |
| Video editing scratch | RAID 0 | Full speed, data can be re-rendered |
| Tight budget, two drives | RAID 1 | Better than nothing |
| 8+ large drives | RAID 6 | Survives a second failure during a long rebuild |
NAS for Plex and backups? RAID 5, four drives, call it a day.
Workstation? Boot drive on RAID 1. Data on whatever you can afford.
Database? RAID 10 or do not bother.
Video editing scratch? RAID 0 is fine, you are re-rendering anyway if it dies.
Broke? RAID 1 with two drives. Better than nothing.
How much usable space do you get from four 1 TB drives?
Four 1 TB drives give 4 TB in RAID 0, 3 TB in RAID 5, 2 TB in RAID 6, 2 TB in RAID 10 and 1 TB in RAID 1. For RAID 6, four drives is the minimum, and RAID 50 needs six. In Windows each 1 TB of usable space shows as roughly 931 GB.
Say you got four 1TB drives. RAID 5 gives you 3TB. RAID 10 gives you 2TB. With RAID 6 four drives is the minimum, and you get 2TB from them.
Two drives in RAID 1? Half goes to the mirror. 2TB total, 1TB usable.
In the calculator you get exact numbers. These are just ballpark.
Does RAID replace a backup?
No. RAID only protects you from a failed drive, usually one or two depending on the level. Delete a file and it is gone from every drive at once, ransomware encrypts the whole array, and a controller failure can sometimes take everything with it. Keep at least one copy of important data somewhere not connected to the array.
Drive dies? RAID handles it. Delete a file? Gone. Ransomware? Encrypted on all drives at once. Controller failure? Sometimes takes everything with it.
RAID protects against hardware failure. That is it. Get a real backup. Cloud, external drive, tape, whatever. Something not connected to the array.
Should you use a hardware RAID card or software RAID?
For most home and small office setups, software RAID is the safer choice. Linux mdadm, Windows Storage Spaces and ZFS let you move the drives to another machine and still read them. Hardware RAID cards from LSI or Adaptec work and are fast, but if the card dies you usually need the same model to get your data back.
Sure, you can buy a hardware RAID card. LSI, Adaptec, whatever. They work, they are fast, but if the card dies you better hope you can find the same model on eBay. Otherwise good luck getting your data back.
Or just use software. Linux mdadm works fine. Windows Storage Spaces exists. Here your CPU does the work instead of a card. Slower? Maybe. But you can move the drives to any machine and they still work.
ZFS nerds will tell you it is the only way to go. They are not wrong. With checksums, bad data gets caught before it spreads. But you need to learn ZFS and throw RAM at it; the RAM calculator helps you size memory for a home server.
Building the server yourself? The PSU calculator counts every hard drive in the power budget, and the PC price calculator shows what an old PC is worth before you turn it into a NAS.