RAID
also: RAID level, software RAID, hardware RAID
RAID (Redundant Array of Independent Disks) is a technique for combining multiple physical hard drives into a single logical unit to improve performance, reliability, or both through data redundancy and/or striping.
RAID combines multiple disk drives to achieve fault tolerance and/or increased performance. Data is distributed across drives using different strategies called RAID levels, each offering different trade-offs between speed, capacity, and redundancy.
Common RAID levels include RAID 0 (striping for speed, no redundancy), RAID 1 (mirroring for full redundancy), RAID 5 (striping with parity for balance), and RAID 10 (mirrored pairs that are striped). For example, RAID 5 spreads data and parity information across three or more drives—if one drive fails, data can be reconstructed from the remaining drives and parity blocks.
On Linux, RAID is typically managed with mdadm (multiple device admin) tool. You can create and monitor RAID arrays with commands like mdadm --create /dev/md0 --level=5 --raid-devices=3 /dev/sda1 /dev/sdb1 /dev/sdc1, which creates a RAID 5 array from three partitions.