Nobody likes to experience a kernel panic on their Mac. This is when your Mac restarts itself while you are working. After it finishes the restart process, you see a dialog telling you that your Mac shut down because of a problem. Worse yet, you may have lost all of your recent work as files are not saved during this type of restart.
We Start Hearing From Our Customers
A kernel panic is even worse when it is happening on your brand new 2019 Mac Pro, a computer that may have cost $10,000 or more. So when we started to hear that a few customers were experiencing kernel panics on their 2019 Mac Pros, we wanted to quickly figure out what was happening. These panics only occurred in a very small percentage of customers who had installed our OWC Accelsior 4M2 cards. The log from macOS said that the kernel panic was caused by an error on the PCIe bus, the wires on the circuit board, which connects cards to the Intel processor. This kernel panic was most often occurring to customers with 2 or more OWC Accelsior 4M2 cards installed.
We Investigate The Problem
Through many hours of dedicated work, our teams figured out what hardware configurations are required for a kernel panic to occur. We worked literally around the clock investigating this problem: when our software development team in California finish testing for the day, our hardware design team in Taipei, on the other side of the world, would pick up where the California team left off.
We determined that the kernel panic occurs when the 2019 Mac Pro sleeps. More importantly, we figured out that the problem only occurs when the OWC Accelsior 4M2 is installed in slots 4 or 5 and only if those slots are configured to use pool B of the PCIe lanes (see below). If OWC Accelsior 4M2 is in any other slot, or if it is configured to use pool A, no kernel panics occur.
The teams also found other cards, which, when installed, result in a kernel panic. One example is the Highpoint SSD7101A.
Getting Help From Our Chip Supplier
We then contacted our PCIe chip supplier in Taiwan to get help determining why macOS thought there was an error on the PCIe bus. Their engineers analyzed the signals on the PCIe bus and told us that macOS was mistakenly indicating that there is an error when, in fact, all the signals were correct.
Apple Starts Investigating
We have since reported this problem to Apple and are working with them to develop a solution. Like the problem we discovered recently — where a Mac hangs while transferring large files — I am confident that they will develop a quick and reliable fix for this problem.
How to Prevent the Kernel Panic From Occurring
Since the kernel panic occurs only when the OWC Accelsior 4M2 is in slots 4 or 5, and the slot is using pool B of the PCIe lanes, the solution for your 2019 Mac Pro is easy. You can either move the card to a different slot or change the slot to use pool A of the PCIe lanes.
Move the OWC Accelsior 4M2 Card to a Slot Other Than Slot 4 or 5
You can move your OWC Accelsior 4M2 card to slots 1, 2, 3, 6, or 7, and this will prevent the kernel panic from occurring. Slot 8 is always occupied by the Apple Thunderbolt card.
Change the Slot With the OWC Accelsior 4M2 Card to Use PCIe Lanes in Pool A
To change the slot which contains the OWC Accelsior 4M2 to use the lanes in pool A, follow these simple steps:
1) Select About this Mac from the menu.
2) Click on the PCI Cards tab in the About This Mac window.
3) Click on the Expansion Slot Utility… button.
4) Click on the Automatic Bandwidth Configuration checkbox to deselect it.
5) Click on the button in the A column next to the slot containing your OWC Accelsior 4M2. (In this example, it is slot 4.)
6) When you are done, the Expansion Slot Utility window should look like this.
7) Click the close box in the top left of the Expansion Slot Utility window. You will be prompted to save your changes, and then your 2019 Mac Pro will restart.