TerraMaster RAID calculator: usable capacity under TOS
By Devin Chua · Data checked by Owen Nakamura · Updated With 4 × 8 TB in TRAID, a TerraMaster NAS keeps about 21.83 TiB usable (24 TB in drive-maker terms), and a single drive failure is survivable. The key is TRAID: it subtracts only the largest drive from the total, so it uses mixed drive sizes too. The calculator below shows only the RAID types TOS actually offers, priced to fill in Canadian dollars.
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SHR (Synology Hybrid RAID)
That is 24 TB the way drive makers label capacity. Your NAS shows you the smaller number because it counts in powers of two.
Drives: from CA$2,016 for 4 × 8 TB (CA$63.01/TB overall)
What TOS does differently with RAID
TerraMaster is, alongside Synology, the only maker in this price band with a genuine flexible RAID. TRAID computes like SHR: only the largest drive comes off the total. TRAID+ matches SHR-2 and survives two simultaneous failures. This calculator models TRAID with the same maths as SHR.
Third-party drives in a TerraMaster NAS
TerraMaster advertises that it locks no drives: 'TerraMaster restricts neither drive brands nor third-party SSDs.' The compatibility list is purely advisory.
Calculate for your exact model
Bay count matters: a two-bay unit cannot do RAID 5, which needs at least three drives. So each TerraMaster model has its own calculator with the bays already set:
And then the drives
Which drives belong in a TerraMaster NAS is covered in the buying guides. The short answer: CMR, not SMR, rated for 24/7 use. Why that is not a detail but decides whether a rebuild succeeds is explained under CMR vs SMR.
Frequently asked questions
Which RAID types does TerraMaster support?
TOS offers TRAID, TRAID+ or TRAID-2, plus Basic, JBOD, RAID 0, 1, 5, 6 and 10, depending on how many bays your model has. A two-bay unit cannot do RAID 5, which needs at least three drives.
Does TerraMaster have an equivalent to Synology's SHR?
Yes, it is called TRAID. It subtracts only the largest drive from the total instead of sizing to the smallest, so mixed drive sizes are genuinely put to use.
Can I put third-party drives in a TerraMaster NAS?
TerraMaster advertises that it locks no drives: 'TerraMaster restricts neither drive brands nor third-party SSDs.' The compatibility list is purely advisory.
How much storage is left with 4 × 8 TB in a TerraMaster NAS?
In TRAID, about 21.83 TiB usable — 24 TB in drive-maker terms. One drive goes to parity and a single failure is survivable. The NAS shows less than the label because makers count in decimal and the NAS in powers of two.
Which drives belong in this NAS?
CMR NAS drives rated for 24/7 use: Seagate IronWolf, WD Red Plus, Toshiba N300 or their Pro variants. SMR drives do not belong in any RAID array, because they collapse dramatically during a rebuild after a failure.
Devin Chua works out which drives, RAM and NVMe cache fit which NAS model at nasdrives.ca, and what the RAID choice means for usable capacity, checked against what is in stock on Amazon.ca.
Data checked by Owen Nakamura, Technical editor (data checking)