A RUT976 was reported to reject two SanDisk 2TB microSDXC cards across firmware 7.19.4 and 7.21, while tested 1TB and 8GB cards mounted successfully under 7.19.4. The evidence does not establish a root cause or confirmed fix. It supports isolating the mount failure from the separate boot-instability symptoms and submitting diagnostic files through the manufacturer's official support channel.
Compare the Observed Firmware Behavior
| Firmware | Card and file system | Observed result |
|---|---|---|
| 7.19.4 | 2TB, exFAT | RUT976 booted, but the card did not mount or display a path in the administration interface. |
| 7.19.4 | 1TB and 8GB, exFAT | Both capacities mounted and displayed a path. |
| 7.21, initial installation | 2TB, 1TB, and 8GB; exFAT or ext4 | The router reportedly failed to boot with each tested card. Card fill level did not change the result. |
| 7.21, after firmware reload | 2TB and 1TB, exFAT | The earlier card-related boot problem initially disappeared, but 2TB still failed to mount while 1TB mounted. |
| 7.21, later boot without a card | No card installed | A subsequent startup stalled with all LEDs on for 15 minutes. The router booted after three hard resets. |
The repeatable capacity boundary in the reported tests is the strongest diagnostic evidence: both tested 2TB cards failed to mount, while the tested 1TB card mounted. This is an observed result, not proof of a general 2TB capacity limit.
Separate Mount Failure from Boot Instability
Under 7.19.4, the 2TB failure was limited to mounting: the router still booted. Hot-replacing the unmounted 2TB card with an 8GB card caused an unexpected reboot; after that reboot, the 8GB card was recognized. ext4 was not tested with 7.19.4.
The initial 7.21 test produced a broader failure. All LEDs flashed continuously, the router did not answer ping, and it remained unstable even after the cards were removed. During recovery it became reachable while flashing, but requests timed out; responsiveness returned after about 20 minutes. Reloading 7.21 changed the immediate result, but later boot instability occurred without any card installed. Therefore, do not assume every boot failure is caused by an inserted microSD card.
Run a Controlled Capacity and Firmware Test
- Establish a clean baseline by booting the RUT976 without a card and confirming that the administration interface responds.
- Record the installed firmware before testing. Keep 7.19.4 and 7.21 results separate because their reported failure modes differ.
- Test one card at a time. Confirm whether the router boots, whether the card appears in the administration interface, and whether a mount path is shown.
- Compare a known mounting capacity with 2TB using the same tested file system where possible. In the available evidence, 1TB exFAT mounted after reloading 7.21 while 2TB exFAT did not.
- Avoid treating hot replacement as a valid workaround: replacing the unmounted 2TB card with an 8GB card under 7.19.4 caused a reboot.
- If the failure persists, collect the troubleshoot, system log, and kernel files after the router becomes responsive and submit them through the manufacturer's official support channel. Review these files for passwords, public IP addresses, serial numbers, or other sensitive data before sharing them.
Define the Supported Conclusion
The evidence confirms a 2TB mount failure with a SanDisk Extreme 2TB microSDXC and a SanDisk Extreme Pro 2TB microSDXC, both rated A2, U3, and V30. It also confirms successful mounting of a SanDisk Extreme Plus 1TB microSDXC with the same listed ratings. These results narrow the investigation to capacity, card-specific behavior, firmware handling, or another implementation issue, but they do not identify which factor is causal.
No resolved firmware version, configuration change, formatting procedure, or hardware replacement is documented. Treat firmware reload as a diagnostic action that changed the boot symptoms, not as a verified correction for the 2TB mount failure.
FAQ
Why does a 2TB microSD card not mount in the RUT976?
The available tests show two 2TB SanDisk microSDXC cards failing to mount on firmware 7.19.4 and 7.21, while a 1TB card mounted. The evidence does not establish whether capacity, card implementation, firmware, or another factor is the root cause.
Does reloading RUT976 firmware 7.21 fix the 2TB microSD problem?
No confirmed fix is documented. Reloading 7.21 initially removed the card-related boot issue, but a 2TB exFAT card still failed to mount and later boot instability occurred without a card installed.
Can I hot-swap the RUT976 microSD card after a mount failure?
The documented hot replacement of an unmounted 2TB card with an 8GB card on firmware 7.19.4 caused the router to reboot. Use a controlled powered-down test unless the manufacturer provides an approved hot-swap procedure.
