ORA Free Tools

RAID capacity calculator

RAID trades raw capacity for protection against drive failure, so a stack of drives never gives you their full combined size. Enter what you're planning to build to see the usable space, how many failures it survives, and how efficiently it uses your drives.

Number of drives Size per drive (TB) RAID level

24 TB usable capacity

32 TB raw capacity

1 drive failures survived

75% space efficiency

RAID 5 uses one drive's worth of capacity for parity and survives a single drive failure.

RAID is not a backup. It protects against a drive dying, not accidental deletion, ransomware, or theft. Always keep a separate backup of anything you can't afford to lose.

Most reliable drives to build with

1 Samsung 990 PRO SSD (2TB) 10.0 Reliability & Endurance $389.99 2 WD_BLACK SN850P NVMe M.2 SSD (PS5 Licensed) 9.8 Reliability & Endurance $219.99 3 Crucial P310 2TB SSD (PCIe Gen4 NVMe) 9.8 Reliability & Endurance $289.90

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Frequently asked questions

What does a RAID calculator tell me?

It shows how much usable storage you get after redundancy. RAID trades raw capacity for protection against drive failure, so a set of drives never gives you their full combined size.

How much space does RAID 5 use for redundancy?

RAID 5 sacrifices exactly one drive's worth of capacity for parity. Four 8 TB drives (32 TB raw) give 24 TB usable and survive one drive failure.

What is the difference between RAID 5 and RAID 6?

RAID 6 uses two drives' worth of parity instead of one, so it survives two simultaneous failures. It costs you more usable space but is safer for large arrays where rebuilds take a long time.

Is RAID a backup?

No. RAID protects against drive failure, not accidental deletion, ransomware, or fire. You still need a separate backup of anything you can't afford to lose.