Apple Xserve (Early 2009): Has anyone installed PCIe SSD in PCI-E slot? I am reconfiguring a working Apple Xserve (Early 2009) [Xserve3,1][model A1279][MB449LL/A] which does not currently have an SSD installed, neither the factory 128GB SATA, nor any aftermarket.  I'm planning to replace the standard 3-drive SATA Drive Interconnect Backplane with the Apple Xserve RAID Card.  The fans howl something fierce, so I plan to replace the Fan Array.  I also plan to replace the single processor Logic Board with the dual processor Logic Board.

It seems to me that performance would be better, and overhead lower if I install a current generation PCIe SSD in the PCI-E Riser Card (ie, PCIe “backplane”), rather than install an Apple circa-2009 SATA SSD (which connects through the Front Panel Board). 

Has anyone successfully installed a PCIe SSD in an Xserve PCI-E Riser Card?
I'm running a 2009 Xserve on a Plextor M6e 256GB (PX-AG256M6e) and it works great. I also just installed 10.11.6 on a Samsung SM951, AHCI version (PN MZHPV256HDGL). As far as I can tell, it must be the AHCI version and not the NVMe version to work. I put it on a StarTech PEX4M2E1 M.2 PCIe adapter. Both of these put the original SSD to shame in terms of performance.