RAID — Redundant Array of Independent Disks

RAID combines multiple disks into one logical drive — for redundancy or speed. No RAID replaces backups!

RAID 0: Striping  — double speed, but ONE disk failure = all data lost
RAID 1: Mirroring — one failure harmless, half capacity
RAID 5: Striping + parity (3+ disks), tolerates 1 failure
RAID 10: Mirror + stripe (4 disks), speed AND safety

Software vs Hardware RAID

Hardware RAID uses a controller; software RAID (Linux mdadm, ZFS) is flexible and today's standard on servers. ZFS adds snapshots and checksums.

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