What causes the orange light on Promise Pegasus 3 R4?

The cables on some of the Promise Pegasus arrays are easy to dislodge, so check the cabling.

Power down the array and the Mac, remove all the disks keeping the disk-in-bay order consistent, clean out the fuzz that tends to build up within, power up without the disks installed, and see if the symptoms of the fault change.

Then power down the array and the Mac, and re-insert the disks maintaining the original disk-in-bay order, power up the array and then the Mac, and see if things improve.

Check around for a Promise diagnostic tool (maybe this?), and then check with Promise support, too.

When I originally got my Promise 3 R4 unit four or five years ago, whenever the Mac went to sleep, this unit also did so. That is, the fans would stop and there appeared to be no activity. A movement of the mouse at that point would wake both the Mac and the Pegasus unit. At some point, a year or two later, I noticed that the Pegasus unit would fail to wake up after sleep or power up after a restart. At that time, I found a fix which was to unplug the Thunderbolt leads from the back of the Pegasus unit, which would cause the fans to spin up and the RAID system to become accessible in finder. Some MacOS updates later and this “fix” ceased to be effective. I was then only able to get access to the RAID system by completely uninstalling all related files/software and drivers. As long as I did not power down the computer, I had no difficulty. However, this caused noise and wasted electricity so I got into the habit of going through the uninstallation and reinstallation of files, drivers and extensions each and every time I switched the Mac back on again after a period of not being in use. Finally, some months ago, I found that this process required several interactions before I could access the RAID drives and finally this ceased to work at all. I ended up disconnecting the drive unit and setting it aside. I am only coming back to this now following uninstalling and reinstallation this evening of a KEXT (or was it DEXT) driver on my Mac. I noticed having done so that there were a number of new entries in the extensions section of the MacOS system section.

A couple of months has passed since I was last able to get this RAID system to start so any advice would be appreciated. 

Promise Pegasus can take a while to restart after sleep, and the Mac can seemingly get ahead of that.

The array-equipped Mac mini boxes I'm familiar with are configured to not sleep, which avoids that whole issue.

After a power failure past the batteries, usually restarting the arrays first, waiting for the arrays to stabilize, and then restarting the Mac, works.

If the array is not functional, then it, or maybe the sockets or the cabling has failed. Check with Promise Support.

I’ve been deploying Synology storage arrays lately, and less Promise gear. Different approach, different wrinkles.