sysop@hub:~/tools/raid-calculator$
raid-calculator
How much space is left, how many disks may fail, and how likely a rebuild is to go wrong. Change a value and everything updates, including a comparison of every level your disks allow.
the disks
every level with these disks
Click a row to switch to that level.
which level for what
| Level | Good for | Think twice when |
|---|---|---|
| RAID 1 | Two disks: boot drives, a small NAS, a single server. | You need more space than one disk holds. |
| RAID 5 / RAID-Z1 | Three or four small disks or SSDs where capacity matters. | The disks are larger than about 4 TB. The rebuild is long and nothing protects it. |
| RAID 6 / RAID-Z2 | The default for hard disks today: file servers, backup targets, NAS with five or more bays. | You need high write speed for databases or many virtual machines. |
| RAID 10 | Databases and virtual machines: fast writes, short rebuilds. | Half the capacity is too expensive. |
| RAID 50 / 60 | Large shelves with twelve disks and more. | You have fewer than eight disks. Plain RAID 6 is simpler. |
| RAID 0 | Scratch space and caches that can be rebuilt. | Anything you would miss. |
RAID keeps a system running when a disk dies. It does not protect against deleted files, ransomware, a failed controller, fire or theft: that is what a backup is for. Plan one with the backup planner. Capacities are decimal, as printed on the disk (1 TB = 1,000 GB), and the operating system shows the smaller binary figure. File system and controller overhead take a few percent more. Rebuild times assume an idle array, under load they can double or triple.
Related: backup planner transfer time calculator backup and disaster recovery checklist