RAID calculator

RAID calculator: what it is for

Choose the RAID level, the number of drives and the size of each, or list drives of different sizes. The calculator shows the usable space in TB and in TiB (as the system displays it), the space used for protection, the space left unused because of the smallest drive and how many drives can fail.

It also warns when the chosen RAID needs more drives or an even number of drives.

How to use

1. Choose the RAID level.
2. Enter how many drives and the size, or list the different sizes.
3. Compare usable space, protection and fault tolerance.

When to use it

• Set up a NAS at home or at the office.
• Choose between RAID 5, 6 and 10 for a server.
• Know how much space you'll have before buying drives.

Frequently asked questions

Which RAID should I choose?

RAID 1 mirrors the data (half the space, very safe, good for 2 drives). RAID 5 loses the space of 1 drive and survives 1 failure. RAID 6 loses 2 drives and survives 2 failures, good for large drives. RAID 10 loses half and survives 1 failure per mirrored pair, with great performance. RAID 0 has no protection at all.

What if the drives are different sizes?

In traditional RAID, every drive is used at the size of the smallest. The calculator does this and shows how much space goes unused. Systems like Synology SHR make better use of mixed drives.

Why does the system show less space than the drive says?

Manufacturers use decimal terabytes (1 TB = 1 trillion bytes) and operating systems show TiB (base 2). A 4 TB drive shows up as about 3.64 TiB. The calculator shows both.

Does RAID replace backups?

No. RAID protects against a drive failure, but not against deleted files, viruses, ransomware or a fault in the NAS itself. Keep a copy somewhere else.

Is it really free?

Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.

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