Fanxiang S660 4TB Review — Four Terabytes of QLC on a Budget (2026)
Quick answer
The Fanxiang S660 4 TB is for the buyer who wants the most gigabytes per dollar in a PCIe 4.0 form factor and is willing to treat the drive as disposable — a Steam library repository, a Plex media drive, or a local backup target where every byte exists elsewhere.
Read: 5000 MB/s Write: 4500 MB/s Endurance: 2800 TBW Warranty: 5 years Interface: M.2 4.0 x 4
The Fanxiang S660 4 TB is the biggest, cheapest PCIe 4.0 drive you can buy — and it is unapologetically QLC, which means you trade write stamina for capacity and hope the price makes up for it.
Controller & Memory
ServeTheHome's teardown of the S660 4 TB confirmed what the controller and performance profile already suggested: Phison PS5021-E21T paired with Micron 176-layer QLC (N48R), no DRAM, 64 MB HMB, and a single-sided M.2 2280 PCB. The drive ships with a heatsink, thermal pads, a screwdriver, and an M.2 screw — the same accessory kit Fanxiang includes across the S660 line.
The S660 family spans 512 GB to 4 TB, all sharing the same E21T-plus-QLC architecture. The 4 TB model is the highest-capacity option and carries the best endurance rating at a confirmed 2,800 TBW. It also has the largest SLC write cache in the family — likely well over 500 GB — which makes it the most resilient S660 against the QLC write cliff in real-world use. If you are going to live with QLC, the 4 TB variant makes the compromises easiest to swallow.
At 4 TB, the S660 competes with the Crucial P3 Plus, Silicon Power UD90, and Team Group MP44Q — all DRAM-less QLC designs. The Fanxiang typically undercuts all three on price, sometimes by a meaningful margin. But at this capacity, the cost of a drive failure is higher simply because there is more data on the line, and Fanxiang's support infrastructure has not scaled to match.
Storage Comparisons:
S660 Performance & Benchmarks
The S660 4 TB is rated for 5,000 MB/s sequential reads and 4,500 MB/s sequential writes, with random IOPS around 600,000 reads and 500,000 writes. The large capacity provides ample NAND dies to saturate these ratings, and the pseudo-SLC cache pool is generous enough that most consumer workloads — even large game installs — complete before the cache fills.
Fanxiang S660 4 TB vs M.2 4.0 x 4 peers
Switch between sequential throughput and random IOPS to see how this drive stacks up against other M.2 4.0 x 4 SSDs in our database. The highlighted bar is the drive on this page — click any other bar to open that drive.
- Patriot Viper PV593 1 TB: 14,500 MB/s read, 14,000 MB/s write
- Patriot Viper PV593 2 TB: 14,500 MB/s read, 14,000 MB/s write
- Patriot Viper PV593 4 TB: 14,500 MB/s read, 14,000 MB/s write
- Patriot Viper PV573 2 TB: 14,000 MB/s read, 12,000 MB/s write
- Fanxiang S660 4 TB (this drive): 5,000 MB/s read, 4,500 MB/s write
When the cache does exhaust, writes degrade through a folding phase at roughly 1,400 MB/s before settling to native QLC speed around 530 MB/s. This is the same behaviour as every other QLC drive in this class; the S660's advantage at 4 TB is simply that the cache is larger, so you hit the cliff less often. For a bulk media library, game repository, or backup target where writes are large but infrequent, this performance profile is acceptable. For a primary workstation drive or any role involving daily large data ingest, QLC remains the wrong tool regardless of capacity.
Fanxiang S660 vs Competitors
See how the S660 stacks up against other M.2 4.0 x 4 drives in our database:
Compare with rival drives:
Endurance, TBW & Warranty
The 4 TB S660 carries a confirmed 2,800 TBW endurance rating and a claimed 5-year warranty. At 50 GB per day, the endurance budget stretches to over 150 years — QLC endurance concerns at this capacity are mathematically irrelevant for consumer workloads. The MTBF is rated at 1.5 million hours, with the standard caveat that this is a population statistic. The real warranty limitation is Fanxiang's support responsiveness: the S660 does not appear on the company's website, RMA requests reportedly go unanswered, and some users have only obtained refunds through retailer intervention. A 5-year warranty from an unreachable company is worth less than a 3-year warranty from a responsive one.
Fanxiang S660 4 TB Specifications
| Category | Value |
|---|---|
| Capacity [?] | 4 TB |
| Interface [?] | M.2 4.0 x 4 |
| Controller [?] | Phison PS5021-E21T 4 Channel |
| Memory type [?] | Micron 176-L QLC |
| DRAM [?] | No |
| Read speed (MB/s) [?] | 5000 |
| Write speed (MB/s) [?] | 4500 |
| Read IOPS [?] | 600000 |
| Write IOPS [?] | 500000 |
| Endurance (TBW) [?] | 2800 |
| MTBF (million hours) [?] | 1500000 |
| Warranty (years) [?] | 5 |
Verdict: Is the S660 Worth It in 2026?
The Fanxiang S660 4 TB is for the buyer who wants the most gigabytes per dollar in a PCIe 4.0 form factor and is willing to treat the drive as disposable — a Steam library repository, a Plex media drive, or a local backup target where every byte exists elsewhere. It is not a primary boot drive, not a workstation scratch disk, and certainly not the place to store the only copy of anything. If that describes your use case, the S660 4 TB delivers unbeatable capacity economics. If it does not, the Crucial P3 Plus 4 TB costs more but comes from a company that still answers the phone.
+ Pros
- 4 TB of PCIe 4.0 storage at the lowest price in its class
- Confirmed 2,800 TBW endurance — ample for any consumer workload
- Single-sided PCB with included heatsink fits laptops and PS5
- Large SLC cache buffer minimises real-world QLC write cliff encounters
- Includes mounting hardware and screwdriver in the box
- Cons
- QLC NAND write cliff drops sustained writes to ~530 MB/s once cache fills
- DRAM-less HMB design limits mixed-workload consistency
- Marketed as TLC on some retailer listings but objectively QLC per Flash ID analysis
- Warranty support practically non-existent — RMA requests go unanswered
- At 4 TB, a drive failure represents a significant data loss if not backed up
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