RAID Capacity Calculator Online

How to Use This RAID Calculator

Select RAID type. Put in your drive count and size. Done. You see the result immediately.

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.

RAID Types

There’s like 6 common ones. Each has tradeoffs. Here’s 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. 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. You’re paying for 2 drives but only getting space of 1. Lots of small business servers run their OS on RAID 1. It just works.

RAID 5

This is what most people end up using. Minimum 3 drives. Parity data gets spread around so if one drive fails, you don’t lose anything. With 4x 1TB drives you get 3TB usable. Good enough for home NAS, file servers, that kind of thing. Just don’t cheap out on the drives.

RAID 6

RAID 5 but paranoid. Two drives can fail at the same time and you’re still fine. Costs you 2 drives worth of space instead of 1. Makes sense when you have 8+ large drives because rebuilds take forever and that’s when drive #2 likes to fail.

RAID 10

Pairs of mirrors striped together. Four drives minimum, half the space. Fast reads, fast writes. Database people swear by it. MySQL shops run RAID 10 on everything.

RAID 50

Enterprise stuff. Multiple RAID 5 arrays striped together. You need at least 6 drives to even start. Faster rebuilds than a huge RAID 5. Most people will never need this.

What Should You Pick

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 don’t bother.

Video editing scratch? RAID 0 is fine, you’re re-rendering anyway if it dies.

Broke? RAID 1 with two drives. Better than nothing.

Quick Numbers

Say you got four 1TB drives. RAID 5 gives you 3TB. RAID 10 gives you 2TB. RAID 6 would need more drives but you’d get 2TB from four.

Two drives in RAID 1? Half goes to the mirror. 2TB total, 1TB usable.

The calculator shows exact numbers. These are just ballpark.

RAID Won’t Save You From Everything

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’s it. Get a real backup. Cloud, external drive, tape, whatever. Something not connected to the array.

Controller Card or No Controller Card

You can buy a hardware RAID card. LSI, Adaptec, whatever. They work, they’re 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. 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’s the only way to go. They’re not wrong. Checksums catch bad data before it spreads. But you need to learn ZFS and throw RAM at it.

FAQ

What even is RAID?

Bunch of drives working together. Sometimes for speed, sometimes so you don’t lose everything when a drive craps out. Been around since the 80s. Still useful.

I have a Synology/QNAP NAS. Which RAID?

Four bays? RAID 5. Two bays? RAID 1 or their proprietary hybrid thing. Don’t overthink it. RAID 5 on a 4-bay NAS is what like 80% of people run.

RAID 5 wastes how much space?

One drive. Always one drive for parity no matter how many you have. Four drives means three usable. Eight drives means seven usable. Math isn’t hard.

Got different size drives, can I mix them?

Bad idea. The big drive gets treated like the small one. Waste of money. Buy the same drives, same batch if you can, same firmware ideally.

Someone told me RAID 0 is fine

For what? Game installs you can redownload? Sure. Anything else? That person is wrong. One drive fails and it’s all gone. Zero redundancy means zero protection.

Drive died in my RAID 5. Now what?

Replace it. The array rebuilds itself. Don’t wait around, another failure during rebuild kills everything. This is the scary part of RAID 5 with big drives.

Rebuild is taking forever

Yeah. Big drives do that. 8TB might take a day or two. Array stays online but slow. Some people run RAID 6 just because rebuilds are less terrifying.

SSD RAID worth it?

Faster everything. Rebuilds happen quick. No spinning parts to break. Costs more per TB though. Mix SSD cache with HDD storage if budget is tight.

What’s stripe size

Chunk of data written before moving to next drive. Big stripes for video files. Small stripes for databases. Default is usually fine, stop tweaking.

Can I add more drives later?

Maybe. Hardware cards usually let you expand RAID 5. RAID 10 wants pairs. ZFS has rules about this. Look up your specific setup before assuming yes.