TerraMaster F4-425: capacity calculator
By Devin Chua · Data checked by Owen Nakamura · Updated In the TerraMaster F4-425 with 4 × 8 TB in TRAID you keep 21.83 TiB usable (24 TB in drive-maker terms), surviving 1 drive failing. The calculator below is preset to the 4 bays and the RAID types TOS 6 actually offers on this model (including TRAID, which uses mixed drive sizes), with the cost to fill in Canadian dollars from live Amazon.ca prices.
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Preset for the F4-425: 4 bays, and only the RAID types this model actually supports.
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 to know about the F4-425
The only alternative to Synology with a genuine SHR counterpart: TRAID uses mixed drive sizes, TRAID+ matches SHR-2 with double fault tolerance. If you have a stack of mismatched drives, you lose less here than with UGREEN or QNAP.
The F4-425 at a glance
| Bays | 4 × 3.5-inch SATA and 2.5-inch SATA SSD |
|---|---|
| Maximum raw capacity | 120 TB 4 × 30 TB, per the manufacturer |
| Processor | Intel N5095 (4 cores, 2.0 GHz) |
| Memory | 4 GB stock, DDR4 SO-DIMM, no ECC (1 slot) 16 GB official |
| M.2 NVMe | none No M.2 slots. Note: NVMe, DDR5 and 5GbE only come with the F4-425 Plus, not this model. |
| Network | 1 × 2.5GbE |
| RAID types | TRAID, TRAID+, Single, JBOD, RAID 0, RAID 1, RAID 5, RAID 6, RAID 10 |
| Third-party drives | unrestricted Open, and TerraMaster advertises it: “TerraMaster restricts neither drive brands nor third-party SSDs.” The compatibility list is purely advisory. |
TRAID: TerraMaster's answer to SHR on the F4-425
TRAID computes like SHR — only the largest drive comes off the total — so the F4-425uses mixed drive sizes instead of leveling to the smallest. TRAID+ matches SHR-2 and survives two simultaneous failures. That makes TerraMaster, alongside Synology, the only maker in this price band with a genuine flexible RAID; UGREEN and QNAP offer nothing like it.
RAID 5 or RAID 6 across the F4-425's 4 bays?
With 4 bays the F4-425 gives you the choice. RAID 5 (or TRAID) leaves 3 of 4 drives as usable capacity and survives one failure; RAID 6 spends one more drive for two. The rule of thumb: from 16 TB drives up, the rebuild after a failure runs so long — easily a full day — that a second failure in that window stops being theoretical. That is when RAID 6 earns its cost on the F4-425.
Which drives belong in the F4-425?
CMR NAS drives rated for 24/7 use — Seagate IronWolf, WD Red Plus, Toshiba N300 or their Pro variants. Our drive picks for the F4-425 with live prices show which of those currently offers the best capacity per dollar. If you are working back from a target capacity instead, the drive-count calculator works out how many drives you need.
Frequently asked questions
How much storage is left in the F4-425 with 4 × 8 TB?
About 21.83 TiB usable — 24 TB in drive-maker terms — computed in TRAID, the sensible default for this model. It survives 1 drive failing. The gap from the 32 TB raw goes to parity.
Which RAID types does the F4-425 support?
TOS 6 offers TRAID, TRAID+, Single, JBOD, RAID 0, RAID 1, RAID 5, RAID 6, RAID 10 on the F4-425. TRAID is the one that matters: it lets the F4-425 use mixed drive sizes instead of leveling every drive down to the smallest.
Can I put third-party drives in the F4-425?
Open, and TerraMaster advertises it: “TerraMaster restricts neither drive brands nor third-party SSDs.” The compatibility list is purely advisory.
How much memory does the F4-425 take?
It ships with 4 GB (DDR4 SO-DIMM, no ECC (1 slot)). 16 GB official There is one slot.
Why does my NAS show less than the calculator says?
Because the maker and the OS count differently. A drive maker calls one trillion bytes a TB; the NAS counts in powers of two and calls that a TiB — about 9 percent less. That is why this calculator leads with the TiB figure: it is the number you will read off the screen.
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)