What is RAID?
RAID is a family of methods combining physical drives into a logical arrangement for performance or fault tolerance.
How it works and where it is used
RAID 0 stripes data but one failed drive can lose the array. RAID 1 mirrors data; parity-based levels need more disks. Actual resilience depends on configuration and how many drives fail together. Controller compatibility, rebuild time and workload also matter.
Limits, safety and selection criteria
RAID is not a backup against deletion, ransomware, fire or silent corruption. Calculate usable capacity and fault tolerance; keep separate backups and test restoration. Rebuilds stress remaining drives, making health monitoring important. With four drives, usable capacity varies greatly by RAID level; adding drive labels does not give usable space. Drives purchased together may age similarly and fail close together. Rebuilding large disks can take hours or longer and may reduce performance. Whether an array can be moved after controller failure depends on implementation. Keep backups outside the array, monitor alerts and rehearse restoration. Consider what happens if a whole chassis, power supply or site fails: redundant disks in the same box do not protect against those shared failures.