Hi everyone,
I am experiencing a strange intermittent issue with a Promise Pegasus32 R6 connected via Thunderbolt 3 to a Mac mini running macOS Tahoe 26.2.
The Pegasus occasionally shuts down very suddenly while the Mac itself continues running normally.
Most importantly, I was able to verify the shutdown on a security camera recording of the server room. The video clearly shows that the Pegasus is operating normally, with disk activity LEDs flashing shortly before the incident. Then, from one second to the next, ALL LEDs on the Pegasus go out simultaneously, including the power-button LED.
There is no gradual shutdown and no indication that only the Thunderbolt connection is lost. Visually, it looks exactly as if someone had suddenly pulled the power plug from the Pegasus.
The Mac mini itself remains powered on and running during the entire event.
The Pegasus is located in an air-conditioned server room at approximately 20°C, so an external overheating problem seems unlikely.
After restarting the Pegasus I generated a Promise Service Report. The RAID itself looks healthy:
- Overall RAID status: OK
- RAID5, 5 x Toshiba MG10 8 TB
- 1 x Toshiba MG10 8 TB global spare
- All six physical drives: OK
- SMART health: OK
- No read/write errors reported
- No bad blocks reported
- PSU status: "Powered On and Functional"
- Fan: Functional
- Controller temperature: 60°C
- Enclosure temperature: 40°C
- 3.3 V / 5 V / 12 V sensors: Operational
The interesting part is the Promise event log. After the most recent incident it reports:
Aug 5, 2026 18:16:11 – Warning – "Last shutdown is abnormal"
followed a few seconds later by:
Aug 5, 2026 18:16:16 – "The system is started (Thunderbolt)"
There is no normal shutdown, host shutdown, host restart or host unplug event immediately before this abnormal shutdown.
Older entries show that the Pegasus is normally able to distinguish between events such as:
- "The system is stopped by host shutdown"
- "The system is stopped by host restart"
- "The system is stopped by host unplug"
This makes the "Last shutdown is abnormal" entry particularly interesting.
I also checked the macOS logs around the event. The Promise DriverKit extension does not appear to crash. macOS reports the Promise device disappearing from the Thunderbolt/PCIe connection, the volume being unmounted, and the Promise driver subsequently terminating normally. When the Pegasus becomes available again, the driver is loaded again. macOS also reports 0 crashes for the Promise driver.
The Mac itself remained powered on throughout the incident.
The Pegasus is currently connected to an APC Back-UPS Pro 900VA, which macOS recognizes correctly via USB. The UPS reported normal AC operation when checked.
As a first troubleshooting step I have now ordered a genuine Apple Thunderbolt 3 cable to rule out the existing Thunderbolt cable.
My main question is:
Has anyone seen a Pegasus32 R6 behave like this – suddenly and completely losing power, with all LEDs including the power-button LED going dark, and subsequently logging "Last shutdown is abnormal"?
Could a Thunderbolt link/cable/controller problem actually cause the Pegasus32 itself to completely power off like this?
Or does the fact that ALL LEDs, including the power LED, disappear instantaneously point more strongly towards an internal PSU/power circuitry problem, or possibly an issue with the external UPS/power supply?
I have the Promise Service Report and can provide additional macOS log excerpts if useful.
Any experience with similar failures would be greatly appreciated.
