RAID has been the standard way to trade storage capacity for either speed or redundancy since 1987, and while cloud storage has reduced how often people set it up themselves, understanding the trade-offs between levels still matters for any real server or NAS build.
RAID 0: Striping, No Redundancy
Data splits evenly across all disks, giving you the combined speed and capacity of every drive — but losing any single disk loses all data on the array. Use only for pure performance scratch storage where the data itself is disposable or backed up elsewhere.
RAID 1: Mirroring
Every disk holds an identical copy of the data. Usable capacity equals just one drive’s size regardless of how many drives you add, but the array survives any single drive failure with zero data loss and no rebuild complexity.
RAID 5: Striping with Distributed Parity
Data and parity information spread across all disks; the array survives any single drive failure, with usable capacity equal to (N-1) drives. The trade-off is a genuinely risky rebuild window after a failure — reading every remaining disk in full to reconstruct the array is exactly the kind of stress that can reveal a second failing drive.
RAID 10: Mirrored Stripes
Combines RAID 1 and RAID 0 — pairs of mirrored disks, striped together. Usable capacity is half your total raw storage, but it delivers both strong read/write performance and the ability to survive multiple drive failures (as long as no mirrored pair loses both members simultaneously), without RAID 5’s risky rebuild.
A Quick Reference
Level Min Disks Usable Capacity Fault Tolerance Use Case RAID 0 2 100% (all) None Scratch/temp, speed only RAID 1 2 50% (1 disk) 1 disk Small, critical data RAID 5 3 (N-1)/N 1 disk General file server RAID 10 4 50% Multiple (usually) Databases, high I/O
The Practical Recommendation
RAID 5 has fallen out of favor for large modern drives specifically because of the rebuild-window risk — RAID 10 or RAID-Z2 (ZFS’s double-parity equivalent) are generally the safer modern choices when you can afford the extra drives, and RAID has never been a substitute for real backups regardless of which level you choose.