RAID Calculator

How it works

RAID combines drives into an array. This calculator uses the smallest drive size as the amount available from each drive. The level determines how much of that array holds data or redundancy.

For example, four 8 TB drives in RAID 5 have 32 TB raw capacity. One drive’s worth is used for parity, leaving an estimated 24 TB before system and filesystem reservations.

Choose a RAID level

• RAID 0: stripes data with no drive-failure protection.
• RAID 1: mirrors data across two drives in this calculator.
• RAID 5: distributed parity; tolerates one drive failure.
• RAID 6: dual parity; tolerates two drive failures.
• RAID 10: stripes across mirrored pairs. One failure is tolerated; additional failures depend on which pair they affect.

Mixed drive sizes

With standard smallest-drive slices, four drives of 8, 8, 6 and 6 TB provide 18 TB in RAID 5. The 4 TB above those slices is unused in this model. Other systems, including proprietary hybrid arrays, can use different layouts.

TB, TiB and actual free space

Drive makers normally use decimal TB (1,000,000,000,000 bytes). TiB uses powers of 1,024. Your device may report less free space after system partitions, filesystem overhead or other reservations.

RAID is not a backup

Redundancy can help an array remain available after certain drive failures. It does not protect against accidental deletion, malware, theft, fire or every hardware failure. Keep separate, tested backups.

Before you choose hardware

This estimate does not check drive compatibility, enclosure support, hot spares, actual performance or recovery. Controllers may require different drive counts. Check the manufacturer’s documentation for your exact setup.

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