RAID levels (0, 1, 5, 6, 10)
RAID combines drives for speed, redundancy, or both. RAID 0 stripes with no protection, RAID 1 mirrors, RAID 5 uses single parity (survives one drive loss), RAID 6 uses double parity (survives two), and RAID 10 mirrors then stripes for speed plus redundancy.
RAID 0 stripes data across drives for maximum throughput and full capacity but loses everything if any one drive fails. RAID 1 mirrors two drives, so a copy survives a single failure at the cost of half the raw capacity. RAID 5 spreads parity across all members and tolerates one failed drive; RAID 6 keeps two parity blocks and tolerates two, which matters as drives grow and rebuilds take longer.
RAID 10 combines mirroring and striping, giving strong random write performance and fast rebuilds while surviving at least one drive loss per mirror pair. Parity RAID (5 and 6) carries a write penalty because each write recomputes parity, and rebuild time on large SATA drives can stretch into days, which is the window where a second failure kills a RAID 5 array.
For a purchased server, match RAID level to workload and drive size. Large-capacity arrays favor RAID 6 over RAID 5 for the second-failure margin. Databases and VM hosts favor RAID 10. Confirm the controller supports the level you want in hardware, and remember RAID is not a backup.
Related
More in Storage
- NVMe: Non-Volatile Memory ExpressNVMe is a storage protocol that lets SSDs talk directly to the CPU over PCIe lanes instead of the older SATA or SAS controller path. It cuts latency and pushes millions of IOPS, far beyond what SATA SSDs deliver.
- SAS vs SATA drivesSAS and SATA are two drive interfaces. SAS-3 runs at 12 Gbps with dual ports, full-duplex signaling, and better error handling for enterprise arrays; SATA III runs at 6 Gbps, single port, half-duplex, and costs less per gigabyte.
- U.2 and U.3 drive form factorsU.2 and U.3 are 2.5-inch enterprise SSD form factors that carry NVMe over PCIe. U.3 uses the newer SFF-TA-1001 connector so one tri-mode backplane bay accepts NVMe, SAS, or SATA; U.2 bays are wired for NVMe or SATA only.
- Hardware RAID vs software RAIDHardware RAID runs on a dedicated controller with its own processor and cache, offloading parity from the CPU and often adding battery-backed write cache. Software RAID (mdadm, ZFS, Storage Spaces) runs on the host CPU with no extra card and no vendor lock to a specific controller.
- DWPD: Drive Writes Per Day (SSD endurance)DWPD measures how many times an SSD's full capacity can be overwritten every day for its warranty period, usually five years. A 1.92 TB drive rated at 3 DWPD tolerates about 5.76 TB of writes per day. Higher DWPD means higher write endurance.
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