TerraMaster NAS Storage: TOS Partitions, TRAID, and Usable Capacity
TerraMaster TOS 5+ reserves approximately 8 GB of system space plus 300 MB per installed drive for boot and swap partitions. This per-drive model is similar to Synology but at a lower rate.
See exactly how much usable storage your configuration delivers.
TerraMaster TOS Storage Overhead
TerraMaster OS (TOS) version 5 and later uses a user-defined system disk architecture. Each installed drive contributes approximately 8 GB system partition + 300 MB boot partition = 8.3 GB per drive. This is a vendor-published figure from TerraMaster's documentation.
On a 4-drive NAS, total system overhead is approximately 33.2 GB. On an 8-drive NAS, approximately 66.4 GB.
TRAID: TerraMaster's SHR Equivalent
TRAID (TerraMaster RAID) uses the same algorithm as Synology's SHR-1. A tiered approach to RAID that maximises usable space with mixed drive sizes. With identical drives, TRAID gives the same result as RAID 5 (one drive of parity, n−1 drives usable).
With mixed drives, TRAID applies the same tier-based calculation as SHR, recovering capacity that standard RAID 5 would waste on the unused portions of larger drives.
RAID Options on TerraMaster
- TRAID. TerraMaster's SHR equivalent. Single redundancy, mixed drive optimisation.
- RAID 5. (n−1) drives usable. Three drives minimum.
- RAID 6. (n−2) drives usable. Four drives minimum.
- RAID 1. Mirror. Two drives minimum.
- RAID 10. Half capacity. Four drives minimum.
- JBOD / RAID 0. No redundancy.
TOS defaults to Btrfs (~4% metadata overhead). ext4 is available as an alternative.
Frequently Asked Questions
Is TRAID compatible with standard RAID tools?
No. Like Synology SHR, TRAID volumes use TerraMaster-proprietary formatting. If you move drives to a non-TerraMaster device, you will not be able to read TRAID volumes directly. RAID 5 volumes (standard mdraid) can be read on any Linux system.
Can TerraMaster expand TRAID arrays by adding larger drives?
Yes. Like Synology SHR, TRAID supports pool expansion by replacing drives with larger ones one at a time. The array rebuilds after each replacement and the pool expands when enough drives have been upgraded.