RAID Capacity Calculator
Pick the RAID level, the number of drives and the size of each. You get the usable space, the share of the raw space and how many drive failures you can survive.
RAID keeps a system running when a drive fails. It is not a backup.
Worked examples
Four 4 TB drives
RAID 5 with four 4 TB drives
12 TB usable, 75% of the raw space, one failure survived
About 10.9 TiB on a computer.
About RAID Capacity Calculator
A RAID capacity calculator tells you how much space an array of drives gives you. RAID joins several drives into one volume. RAID 0 spreads data across all of them for speed and uses all the space, but loses everything if one fails. RAID 1 keeps a full copy on each drive. RAID 5 gives you the space of all the drives but one and survives one failure. RAID 6 gives you all but two and survives two. RAID 10 mirrors pairs and stripes across them, giving half the space.
Pick the level, the number of drives and the size of each. You get the usable space, the share of the raw space, how many drive failures the array survives, and the space in tebibytes, the way many computers show it. The tool also checks the minimum number of drives for each level. RAID helps a system keep running when a drive fails, but it is not a backup.
How to use RAID Capacity Calculator
- Choose the RAID level.
- Enter the number of drives.
- Enter the size of each drive in terabytes.
- Read the usable space and the failures survived.
Common uses
- Planning a home server or NAS
- Choosing between RAID 5 and RAID 6
- Checking what a mirrored pair gives
- Buying drives for a small office
Frequently asked questions
How much space does RAID 5 give with four 4 TB drives?
12 TB, which is three quarters of the 16 TB raw space. It survives one failed drive. A computer shows this as about 10.9 TiB.
What is the difference between RAID 5 and RAID 6?
RAID 6 uses two drives for protection, so it survives two failures but gives up more space. It is more reliable for larger arrays, as a rebuild can take many hours.
What does RAID 10 need?
At least four drives, and an even number, as they work in mirrored pairs. With four 4 TB drives you get 8 TB.
Is RAID a backup?
No. RAID keeps the system running when a drive fails, but deleted files, a virus or a fire affect every drive. Keep a separate copy of important data.
Why does a drive look smaller than its label?
Makers count 1 TB as 1,000,000,000,000 bytes, but many computers use binary units, where a TiB is 1,099,511,627,776 bytes, so a 4 TB drive appears as about 3.6 TiB.