Just read an interesting review of a PCIe card which accepts four flash blades:
http://barefeats.com/hard210.html
Intro from the article:
"Our readers have been frustrated by the inability to get more than 1500MB/s from Samsung SM951 flash blades mounted in slots 3 and 4 of the 2009-2012 Mac Pro tower. The x16 slot 2 has not been a helpful -- until now. One of those frustrated readers turned us on to a new x16 PCIe M.2 carrier board by...
Amfeltec x16 PCIe with 4 SSDs: 5900+ MB/s
http://barefeats.com/hard210.html
Intro from the article:
"Our readers have been frustrated by the inability to get more than 1500MB/s from Samsung SM951 flash blades mounted in slots 3 and 4 of the 2009-2012 Mac Pro tower. The x16 slot 2 has not been a helpful -- until now. One of those frustrated readers turned us on to a new x16 PCIe M.2 carrier board by...
Amfeltec x16 PCIe with 4 SSDs: 5900+ MB/s