A month or so ago, a Promise32 R4 unit stopped powering up... I had repeatedly unplugged and replugged the power cord, the Thunderbolt cable, and the drive sleds. Dead, dead, dead. Even after a full day of being unplugged, it would not power up, so I assumed the power supply had failed. I went through an unnecessarily lengthy process to get an RMA to send it in for warranty repair, and eventually it was returned with "works properly, nothing wrong" notification.
Even before that problem, every time I rebooted my computer, the only way to get the Promise to mount was to turn it off, then unplug it, then plug it back in. It NEVER turned back on automatically, and it NEVER turned on with the manual power button. Only unplugging and re-plugging it would make it turn on. Eventually even that stopped working. So I sent it in, Promise said nothing was wrong, and they sent it back. I plugged it in, and it powered up.
Now, a month later, after rebooting my computer, again the Promise will NOT power back up, no matter what I do. Exact same problem. This is beyond irritating, as this RAID is the most critical component in our system here. Over the years, I've owned probably 5 different RAID enclosure types/brands, and Promise has consistently taken the longest to re-mount after a computer restart...sometimes taking up to 2-5 minutes to mount. But this problem with the power is inexcusable.
Update: 24 hours later, the "fine, nothing wrong with it" (according to Promise) unit still will not power up after having been unplugged for an entire day.