RAID (storage)
Also known as: RAID, redundant array of independent disks, RAID array
RAID (redundant array of independent disks) is a way of combining multiple drives into one storage system for better reliability, speed, or both.
RAID 1 mirrors data on two drives, so if one fails, the other keeps working. RAID 5 and RAID 6 spread data and recovery information across several drives, and RAID 10 combines mirroring and striping. It's common in servers and network storage devices. While RAID keeps systems running through drive failures, it doesn't protect against deletion, ransomware, or theft, so it's never a substitute for backups.
RAID (storage), explained at three levels
At home
RAID 1 is like writing your notes in two notebooks at once. If you lose one, you still have the other. But if you write something wrong, both notebooks have the mistake.
At work
RAID keeps servers and storage running when a drive fails, avoiding downtime.
At home
Many home network storage boxes offer RAID 1 with two drives. It protects against one drive failing, but you still need a separate backup.
At work
Common levels include RAID 0 (speed, no protection), RAID 1 (mirroring), RAID 5 (one drive can fail), RAID 6 (two drives can fail), and RAID 10 (mirroring plus striping).
At home
Drives bought together often fail around the same time. In my opinion, replace a failed RAID drive quickly, before a second one goes.
At work
Monitor drive health and alert on failures, keep spare drives, consider rebuild times for large drives, avoid unsuitable drive types in arrays, and always back up RAID volumes separately.
Real-world examples
At home
Thomas's home storage box used RAID 1. When one drive failed, his photos stayed available while he replaced it, though he still kept a cloud backup.
At work
Fatima's Halifax MSP found a client's server running RAID 5 with a failed drive nobody had noticed for months. She replaced it and added alerts.
How it compares
| feature | RAID (storage) | 3-2-1 backup rule |
|---|---|---|
| Protects against | Drive failure | Deletion, ransomware, disasters |
| Keeps history | No | Yes, older versions |
| Location | Same device | Multiple locations |
| Main benefit | Uptime | Recovery |
RAID keeps you running. Backups get your data back.
For analysts
When reviewing storage, I'd confirm RAID status monitoring and separate backups exist. Many small businesses assume RAID alone protects them.
History & origin
David Patterson, Garth Gibson, and Randy Katz at the University of California, Berkeley, described RAID in a 1988 paper titled 'A Case for Redundant Arrays of Inexpensive Disks,' proposing that many cheap drives could outperform expensive large ones. The industry later changed 'inexpensive' to 'independent.' RAID became standard in servers through the 1990s and in home and small business network storage devices in the 2000s. As drives grew to many terabytes, rebuilding a failed RAID 5 array took longer and carried more risk, pushing many to RAID 6 or other approaches. Newer file systems such as ZFS built similar protections into the file system itself. In my view, 'RAID is not a backup' is one of the most important sentences in IT.