Convert storage units, or work out how much usable space an array of disks gives you after RAID and filesystem overhead.
How to Use
Unit conversion, or RAID capacity.
A size and unit, or the number and size of disks and the RAID level.
Usable space in both decimal (TB) and binary (TiB) units.
VPS & Linux
Disk makers count in decimal units: 1 TB is 1,000,000,000,000 bytes. Linux tools such as df -h and most operating systems count in binary units, where 1 TiB is 1,099,511,627,776 bytes, and often still label them TB. The same 4 TB disk is 3.64 TiB. Nothing is missing.
Each RAID level trades capacity for protection. ZFS RAIDZ works like RAID 5, 6 and triple parity but checks every block, so it can also repair silent corruption.
| Level | Usable space · survives |
|---|---|
| RAID 0 | All disks · no failures |
| RAID 1 | One disk · all but one |
| RAID 5 / RAIDZ1 | All but one disk · 1 failure |
| RAID 6 / RAIDZ2 | All but two · 2 failures |
| RAIDZ3 | All but three · 3 failures |
| RAID 10 | Half · 1 per mirror |
ext4 reserves 5% of each filesystem for root by default, so normal users see a disk as full before it is. On large data disks this can be lowered with tune2fs -m 1. ZFS should be kept under about 80% full for good performance.
RAID Levels and Units
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