OWC Accelsior issue

Hi,

I've been running a 480GB PCI Express Mercury Accelsior SSD E2 in my Mac Pro 4,1 for the past 10 months without any issues. It's setup with a partition for my system drive and another for Parallels images. Overall performance has been extremely impressive to date, however over the last couple of weekends I've experienced a couple of events which has resulted today in the Accelsior refusing to be seen by the system.

My Mac tends to be on 24-5 through the working week due to the different hours I work for different clients and providing I have no work planned for the weekend I don't shut it down until Friday evenings. Last Sunday I fired the machine up and immediately spotted how slow it was to start, then I heard one of the hard disks chugging away. When Yosemite had started I could see it had booted off of the internal SATA backup disk (I take weekly copies of my Main drive with SuperDuper).

Opened Finder and the Accelsior partitions were nowhere to be seen. Rebooted a few times with no difference. After a bit of googling performed a Command+Option+P+R to reset PRAM and this seemed to do the trick. System booted off of the Main partition on the Accelsior and Yosemite was up and running in a few seconds with all partitions present and correct.

This Friday evening I shut the system down after it'd been on all week and today when I fired it up, the Accelsior had once again vanished. This time however, I've been unable to get it to be recognised despite resetting PRAM, swapping it into different PCI slots, removing everything apart from Accelsior and video card. When i remove the backup disks, the system halts at the flashing question mark folder image.

With the side off I watched the Accelsior card when the system is powered on and there is some red LED activity on each of the 240Gb blades but this stops before the system 'chime'.

When I check in 'system information' under SATA/SATA Express. I see my internal hard drives AND DVD each under an Intel ICH10 AHCI and above that, 8 Generic AHCI Controller entries with one of them having a sub entry of MARVEL VIRTUALL. Normally under SATA/SATA Express I have information about the Accelsior but not any longer. When I remove the Accelsior card the Generic AHCI Controller entries vanish so something is being detected.

I'm a bit stumped as nothing has changed system wise apart from the machine being switched off for 36 hours.

Thanks in advance for any suggestions or ideas of what to try next. (I've logged a support ticket with OWC)

Steve.