1) What happens if you use bigger block sizes, say 16M?
2) Which filesystem you're using? Can it be fragmented? Can you test with raw disk to eliminate any filesystem influence?
3) Is dd running on same NUMA node (CPU socket) as your ioDrive2 PCI-e link?
4) To expand on 3, is there chance for QPI saturation (traffic between CPU sockets)? Have you ensured all the software uses CPU local RAM whenever possible and not access other CPU socket's RAM?
5) Are you sure all PCI-e lanes are active? (Try lspci)
Also:
Did you low-level format to 4K blocks, or is is still using 512 byte blocks?
Various options for the kernel module also have a significant effect, as do BIOS settings (C-states, etc.).
I got 2.5-2.9 GB/sec (iirc) with a FusionIO ioDrive2 Duo. It has been more than a year so I do not remember all the details.
Some questions:
1) What happens if you use bigger block sizes, say 16M?
2) Which filesystem you're using? Can it be fragmented? Can you test with raw disk to eliminate any filesystem influence?
3) Is dd running on same NUMA node (CPU socket) as your ioDrive2 PCI-e link?
4) To expand on 3, is there chance for QPI saturation (traffic between CPU sockets)? Have you ensured all the software uses CPU local RAM whenever possible and not access other CPU socket's RAM?
5) Are you sure all PCI-e lanes are active? (Try lspci)