RAID combines several drives into one logical unit to improve performance, protect against drive failure, or both. The level you choose decides how your data is spread across disks and what happens when one fails. Here is a plain-English guide to the levels you will actually meet on servers.
What RAID Is and Isn't
RAID stands for Redundant Array of Independent Disks. It keeps a server running through a drive failure and can boost throughput, but it is not a backup. RAID protects against hardware failure, not against deletion, corruption, ransomware, or a fire in the rack. You still need separate backups.
RAID 0 (Striping)
RAID 0 spreads data across two or more drives with no redundancy. Reads and writes are fast because work is split across disks, and you get the full combined capacity. The catch is brutal: if any single drive fails, the entire array is lost. Use it only for scratch data you can afford to lose.
RAID 1 (Mirroring)
RAID 1 writes the same data to two drives at once, so a complete copy lives on each. If one drive dies, the other carries on with no data loss. You sacrifice half your raw capacity, but the simplicity and resilience make it a popular choice for boot drives and small servers.
RAID 5 (Striping with Parity)
RAID 5 stripes data across three or more drives and adds distributed parity, so the array survives a single drive failure while using only one drive's worth of capacity for protection. It balances capacity, performance, and resilience well, though rebuilds after a failure can be slow and stressful on large drives.
RAID 6 (Double Parity)
RAID 6 is like RAID 5 but with a second parity block, so it can survive two simultaneous drive failures. That extra safety matters for large arrays where rebuilds take a long time and a second failure during rebuild is a real risk. The trade-off is a little less usable capacity and slower writes.
RAID 10 (Mirror + Stripe)
RAID 10 combines mirroring and striping: pairs of drives are mirrored, then striped together. You get strong performance and fast rebuilds while tolerating a drive failure in each mirrored pair. The cost is that you only get half your raw capacity, but for busy databases it is often the best choice.
Which Level Should You Choose?
For a simple boot or low-volume server, RAID 1 is hard to beat. For bulk storage where capacity matters, RAID 5 or RAID 6 stretches your disks further, with RAID 6 preferred as drives get larger. For demanding, write-heavy workloads like databases, RAID 10 gives the best mix of speed and resilience.
How Noded Can Help
Choosing a RAID level is a balance of capacity, speed, and how much risk you can accept during a rebuild. Tell us about your workload and the drives you are using, and we will help you pick a layout and a backup strategy that fit together.
FAQ
Is RAID a backup?
No. RAID protects against drive hardware failure but not against accidental deletion, corruption, malware, or disaster. Always keep separate, ideally offsite, backups alongside any RAID setup.
What is the difference between RAID 5 and RAID 6?
RAID 5 uses one parity block and survives one drive failure, while RAID 6 uses two and survives two failures. RAID 6 is safer on large arrays where rebuilds take long enough that a second failure becomes likely.
Why do people choose RAID 10 for databases?
RAID 10 offers high read and write performance with fast rebuilds and good fault tolerance. Databases are write-heavy and latency-sensitive, so the speed and quick recovery are worth the loss of usable capacity.
Can I expand a RAID array later?
Sometimes, depending on the controller and level, but it can be slow and risky. Plan capacity ahead where possible, and always have current backups before reshaping an array.