RAID and ZFS Calculator
See how much usable space you'll have left with RAID, ZFS, or Unraid, and how many disks are allowed to fail. Includes TB to TiB conversion below.
| Configuration | Usable | In TiB | Loss | Can fail | Note |
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With RAID or ZFS you use multiple disks together, so your files remain safe if a disk fails. The more disks that can fail, the less space you have left. With identical disks, RAID and ZFS use the smallest disk as the measure; Unraid and Synology SHR can make better use of disks of different sizes.
Manufacturers calculate in TB (1012 bytes), your computer shows TiB (240 bytes): a disk of 8 TB therefore shows as approximately 7.28 TiB. ZFS also keeps about 3 percent free for the system; that is included in the figures. RAID is not a backup: a deleted file or a virus is also on all disks.
Convert TB to TiB
Why is my disk smaller than stated on the packaging? Convert here between decimal (TB) and binary (TiB) units.
Manufacturers calculate with decimal units: 1 TB is 1,000,000,000,000 bytes. A TiB is 1,099,511,627,776 bytes, approximately 10% more. A disk of 4 TB is therefore 3.64 TiB. Windows shows that 3.64 as “3.64 TB”, while it is actually TiB. macOS and many NAS systems do show the decimal value. So nothing is lost: the difference is in the unit.