PCI-E SSD cards

[Rob Rati]

I was looking at adding an ssd for a zil and/or l2arc to my zfs pool but all my hard drive bays are full.  I have free pci-e slots, so I started looking at using that instead of a physical drive.  Does anyone have any experience with these ssd pci-e cards in FreeBSD? Do they work without issue, or are there specific ones I should [not] try to use?

On a technical point, there are a lot of these ssd cards in the m.2 form factor.  Using that form factor would allow me to use multiple ssd cards and get some zil mirroring for resiliency.  What I haven't been able to tell is what type of slot accepts an m.2 form factor card.  I know there is the sata-to-sata vs pcie-to-pcie type issue, but everything I have found seems to imply that the m.2 form factor card would fit into a pci-e 1x-16x slot.  Is that correct?  Does it matter how new the MB is if it has pci-e slots?

Rob