RAID Calculator
This RAID calculator shows the usable capacity of every level for your number of drives: four 4 TB drives give 12 TB (10.9 TiB) in RAID 5, for example, and one drive may fail. All levels are listed side by side.
Source: Wikipedia – RAID (Redundant Array of Independent Disks). Updated: .
How it is calculated
A RAID combines several hard drives into one array to gain capacity, speed or fault tolerance, and the usable size depends on the level. For your number and size of drives the calculator shows all common levels at a glance, with space efficiency and allowed failures.
The levels at a glance
RAID 0 spreads data across all drives (striping): full capacity and speed but no safety. RAID 1 mirrors data across drives; only one drive of space is usable. RAID 5 stores one parity and loses one drive of capacity, RAID 6 stores two parities and survives two failures. RAID 10 combines mirrored pairs with striping and needs an even number of drives, four or more. JBOD simply chains drives together.
Example and units
With four 4 TB drives RAID 0 and JBOD offer 16 TB, RAID 5 12 TB, RAID 6 and RAID 10 8 TB each, and RAID 1 just 4 TB. Manufacturers count in terabytes (10¹² bytes), while operating systems often show tebibytes (2⁴⁰ bytes): 12 TB is about 10.9 TiB.
- With mixed drive sizes the smallest counts; the rest stays unused.
- Large drives take long to rebuild in RAID 5; RAID 6 is safer then.
- RAID is not a backup: deletion, ransomware and fire hit all drives.
Frequently asked questions
How much capacity is left with RAID 5?
The capacity of n − 1 drives remains. With four 4 TB drives that is 12 TB; one drive is used for parity.
What is the difference between RAID 5 and RAID 6?
RAID 5 survives one failed drive, RAID 6 survives two thanks to the second parity but costs another drive of capacity. For large drives RAID 6 is usually safer because of the long rebuild time.
Does RAID replace a backup?
No. RAID only protects against drive failure. Accidental deletion, malware, controller faults and theft hit all drives at once; only a separate backup helps against those.
Sources and legal basis
- Wikipedia – RAID (Redundant Array of Independent Disks)
- Wikipedia – Standard RAID levels
- Wikipedia – Binärpräfix (TB and TiB)
As of: · Editorial policy
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