Promise Pegasus2 R6 (Thunderbolt 2) causes Controller Reset/Kernel Panic on Write in Proxmox VE 8 (Mac Mini 2012)

[favonion]

Hardware:

• Host: Mac Mini Late 2012 (Server), i7-3720QM, 16GB RAM.
• DAS: Promise Pegasus2 R6 (6-Bay).
• Connection: Thunderbolt 2 (Native).
• Drives: 6x Mixed HDDs (4TB WD Red, 2TB Toshiba). Configured as JBOD/Pass-Thru.
• OS: Proxmox VE 8.1 (Debian 12 Bookworm), Kernel 6.8.x.

The Issue:I am attempting to use the Pegasus2 R6 as a JBOD enclosure for a MergerFS pool. The drives are visible in lsblk, but any write operation (mkfs.ext4, wipefs, dd) triggers a controller handshake failure, causing the specific drive device to go offline or the entire host to hang/freeze. Read operations seem stable initially, but writes kill the connection immediately.

Symptoms & Logs:

• lsblk correctly lists all 6 drives (e.g., sdb through sdg) upon boot.
• boltctl shows the device as authorized.
• Attempting mkfs.ext4 /dev/sdb results in No such device or address immediately after execution.
• dmesg output during the crash:
  
  sd 0:0:1:0: [sdb] tag#639 aborting command<br>scsi host0: resetting host<br>stex(0000:09:00.0): no signature after handshake frame<br>stex(0000:09:00.0): resetting: handshake failed<br>sd 0:0:1:0: Device offlined - not ready after error recovery<br>
• Initial boot showed PCI resource allocation errors, fixed via GRUB parameters (see below).

Troubleshooting / Steps Taken:

1. Hardware Verification (macOS):
   
   • Booted external macOS Catalina via USB.
   • Installed Promise Utility.
   • Cleared all Arrays and Spare definitions.
   • Set all 6 Physical Drives to PassThru mode.
   • Result: Hardware is functional. Successfully partitioned and formatted all 6 drives (GPT/ExFAT) using macOS Disk Utility. No I/O errors under macOS.
2. Proxmox/Linux Configuration:
   
   • Installed bolt, mergerfs, fuse3.
   • Authorized UUID via boltctl enroll.
   • Added pci=realloc to GRUB_CMDLINE_LINUX_DEFAULT to fix initial "bridge window" allocation errors.
   • Driver loaded: stex: Promise SuperTrak EX Driver version: 6.02.0000.01.
3. Attempted Fixes for Write Instability:
   
   • Tried disabling MSI/AER via pci=nomsi pci=noaer (Result: update-grub hangs because os-prober chokes on the unstable drives).
   • Forced PCI rescan (echo 1 &gt; /sys/bus/pci/rescan) brings drives back after crash, but they die again on next write.
   • Tried mkfs.ext4 -E nodiscard to rule out TRIM/Discard issues. Failed.
   • Tried wiping signatures via dd if=/dev/zero .... Failed (I/O error).

Hypothesis:The mainline Linux stex driver appears incompatible with the Pegasus2 firmware or Thunderbolt tunneling behavior under load (specifically writes), causing the controller to hang during handshakes. It works perfectly in macOS, ruling out cables/backplane.

Question:Has anyone successfully stabilized a Pegasus2 R6 on modern Linux kernels (6.x)? Are there specific kernel parameters or stex module options required to prevent the handshake timeouts?