Originally Posted by unityole
z370 and z390 are the same in that regards, 24 pcie lanes, 3x m.2 slot, if all 3 m.2 are used then 4 sata ports will not work. i would recommend to run m.2 ssd via cpu lanes instead. not only you get lower latency without having to go through chipset you also dont lose any sata ports. you will lose pcie lanes though and single GPU is more than enough.
Is the difference noticeable when running m.2 ssd via the cpu lanes vs the chipset? I know the chipset gets bottle necked by DMI as well but I haven't seen much on how badly as it kinda depends on what other devices are using the chipset. The thing is with this board at least if you use the second slot the GPU slot speed gets downgraded to 8x which I've seen reduces FPS in games by like a little less than 10% using a gtx 1080 ti.
As far as OP's question goes, according to the motherboard manual. http://download.gigabyte.us/FileList...ter_1001_e.pdf
Due to the limited number of lanes provided by the Chipset, the availability of the SATA connectors may be affected
by the type of device installed in the M2. sockets. The M2M connector shares bandwidth with the SATA3 4, 5
connectors. The M2A connector shares bandwidth with the SATA3 1; the M2P connector shares bandwidth with
the PCIEX4 connector. Refer to the following tables for details.
If you look at the diagrams, you can actually use all sata ports if you install a m.2 ssd in the middle m.2 connector (m2a) it will just share bandwidth on the first sata port or if the ssd is small enough to fit in the bottom m.2 (m2p) it will share bandwidth with the bottom pcie port. If your m.2 ssd won't fit in the bottom slot you could just get a m.2 pcie adapter and put it in the bottom pcie slot that way you don't share bandwidth with the sata drives (although they do ultimately get shared over the DMI).