What RAID storage is and what it is not
RAID (Redundant Array of Independent Disks) groups physical drives into one logical volume so a server can read and write in parallel or keep serving after a disk dies. The level you pick decides the trade: speed, usable capacity, and how many drive failures the array survives.
RAID is not a filesystem and not a backup. The operating system sees a single block device and the controller decides where each block lands. Drives used individually, each exposed as its own volume with no redundancy, are called JBOD.
How striping, mirroring and parity work
Striping splits data into blocks and writes them across drives in parallel; mirroring writes the same block to a second drive; parity stores a calculated value that can rebuild one missing block. Every RAID level is a combination of these three.
Parity costs write speed, because each write recalculates and rewrites parity. Mirroring costs capacity, because half the raw space holds the copy. Striping costs neither, which is why RAID 0 is fast and offers no protection at all.
RAID 0, 1, 5, 6 and 10 compared
RAID 0 is fastest with no protection, RAID 1 mirrors every block, RAID 5 survives one failure at (N−1)/N capacity, RAID 6 survives two at (N−2)/N, and RAID 10 mirrors then stripes for fast writes on half the raw capacity.
| Level | Minimum drives | Usable capacity | Survives | Write speed | Best for |
|---|---|---|---|---|---|
| RAID 0 | 2 | 100% | No drive failure | Fastest | Scratch space and caches you can rebuild |
| RAID 1 | 2 | 50% | One drive | Moderate | Boot volumes and small critical data |
| RAID 5 | 3 | (N−1)/N | One drive | Slower, parity on every write | File servers on smaller drives |
| RAID 6 | 4 | (N−2)/N | Two drives | Slowest, double parity | Large drives, archives, NAS |
| RAID 10 | 4 | 50% | One per mirror pair | Fast | Databases and busy virtual machines |
Two rules follow. Never put data you cannot rebuild on RAID 0, and move to RAID 6 or RAID 10 once drives reach roughly 8TB to 10TB, where a RAID 5 rebuild runs for hours with no protection left. WebJi®'s dedicated server hosting ships RAID 1 or RAID 10 for data volumes, with RAID 0 kept for scratch space.
What happens when a disk fails in a RAID array
The array falls into degraded mode: it keeps serving from the surviving drives, reads stay usable, writes slow sharply, and no redundancy remains. Replace the failed drive and the controller rebuilds its contents from the mirror or from parity.
Every remaining drive is read in full during that rebuild. On a large RAID 5 array the window can run for hours, and a second failure inside it ends the array — the practical reason RAID 6 exists.
Hot spares and array rebuilds
A hot spare is an idle drive already installed in the server that the controller rebuilds onto automatically when a member fails, so the unprotected window does not wait for a replacement part.
Rebuild speed depends on drive size, array load and controller. Leave monitoring switched on, hold heavy batch jobs until the rebuild finishes, and confirm the array reports optimal health before you trust it again.
Hardware RAID vs software RAID
Hardware RAID runs on a dedicated controller with its own cache, so the array operates independently of the operating system. Software RAID uses the server's CPU through Linux mdadm, Windows Storage Spaces or ZFS, and adds no hardware cost.
For typical hosting workloads software RAID is enough and moves more easily between machines. Hardware RAID earns its price on write-heavy databases and on servers where the boot volume itself must survive a disk loss. Firmware RAID on a motherboard, sometimes called fake RAID, hands control to a driver after boot — judge it as software RAID.
Why RAID is not a backup
RAID protects availability, not data. A deleted file is deleted from every member drive at once, ransomware encrypts the array exactly as it would a single disk, and fire or theft takes all copies together.
The division of labour: RAID keeps the server serving through a hardware failure, and a backup gets data back after anything else. Keep copies off the same machine and offsite, and test a restore before you need one. For the drives themselves, the SSD versus SATA comparison covers the performance side.
Frequently Asked Questions
What is RAID in simple terms?
RAID joins two or more drives into one logical volume. Striping spreads data for speed, mirroring copies it for safety, and parity rebuilds a lost drive from the others.
What is the difference between RAID 0, 1, 5 and 10?
RAID 0 stripes with no protection, RAID 1 mirrors two drives, RAID 5 adds distributed parity and survives one failure, and RAID 10 mirrors then stripes for fast writes and one failure per pair.
Which RAID level is best for a web server?
RAID 10 for databases and heavy write workloads, RAID 1 for small boot volumes, and RAID 5 or 6 for file storage. Match the level to the workload rather than picking the highest number.
Does RAID replace backups?
No. RAID keeps a server running when a drive fails. It cannot undo deletion, ransomware, file corruption or a lost site, so keep a separate offsite backup.
What happens when a disk in a RAID array fails?
The array runs degraded with slower writes and no further protection until the drive is replaced and rebuilt. A second failure before the rebuild finishes can destroy the array.
What is a hot spare in RAID?
A hot spare is an idle drive in the server that the controller rebuilds onto automatically when a member drive fails, shortening the unprotected window.
Is RAID 5 still safe with large drives?
RAID 5 tolerates one failure, but a rebuild on a 16TB drive can run for hours and a second failure in that window loses the array. RAID 6 or RAID 10 is safer at that size.
Does a dedicated server need RAID?
Yes for any server carrying live data. WebJi® ships dedicated servers with RAID 1 or RAID 10 for data volumes, so a single disk failure does not take the site down.
Is WebJi® an Indian company?
Yes. WebJi® is headquartered in Jaipur, Rajasthan and has operated since 2005. Billing, support and governance all run from India.
Do you provide GST invoices?
Every purchase and renewal gets a GST invoice with our GSTIN, and hosting prices are quoted exclusive of 18% GST. Claim input credit as applicable.