Delete Old Files Threshold - Lesson Learned.
The past several months, I kept running into errors regarding storage drive not keeping up with SS. It always happened when the drive RAID was nearing full. It never was a problem, but keep recurring. I had to manually erase my array. I tried APFS vs HFS. No difference. I switched RAID modes. It seemed my drives were simply no longer fast enough to keep up with deleting files and writing files at the same time.
Then it dawned on me. I've always had a manually set threshold for file deletion. That was set to leave a small fraction of the storage drive free, BUT the number of cameras and bitstream rates has been growing over the years. The daily write total was getting big compared to the free space I had manually specified.
Bumping up the space to be kept free to about 1/2 day of data seems to have solved the issue. Drive is once more keeping up with writing and deleting!
I know there is also an option to let SS automatically set the deletion threshold. That likely would have prevented my problem. If you use a manual deletion threshold, watch out for how your daily write total compares to that space. I surmise that if that free space gets too small, SS writes out too much data before SS gets a chance to delete the next cadres of old files. As a result, available drive space goes to zero and you no longer get any effective recording happening.