What does usable RAID capacity mean?
Usable RAID capacity is the amount of storage available after accounting for mirroring, parity, reserved space, and capacity that cannot be used because drives are different sizes.
RAID Calculator
Visually compare HDD and SSD capacity across common RAID types, including usable storage, protection, system reserve, and unused space from mixed drive sizes.
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RAID protects uptime.
It helps survive drive failure, but it is not a backup.
Mixed SSD sizes matter.
Traditional RAID is limited by the smallest drive, so extra capacity can become unused.
RAID 5 and RAID 6 need parity.
RAID 6 trades more capacity for stronger failure tolerance.
RAID Capacity Questions
Why do mixed drive sizes waste space?
Many traditional RAID layouts calculate capacity from the smallest drive in the set. Extra space on larger drives may be unavailable in that array.
Is RAID the same as a backup?
No. RAID can help keep a system running after a drive failure, but it does not protect against deletion, corruption, ransomware, theft, or site-wide loss.