The motherboard M.2 slot #2 shares bandwidth with a SATA 6.0 Gb/s port. When the M.2 slot is populated, one SATA 6.0 Gb/s port

[IndigoGo]

I am on PCPartPicker and this issue appears in the compatibility check:

"The motherboard M.2 slot #2 shares bandwidth with a SATA 6.0 Gb/s port. When the M.2 slot is populated, one SATA 6.0 Gb/s port is disabled."

My Build:

PCPartPicker part list / Price breakdown by merchant

CPU: AMD - Ryzen 5 1600 3.2GHz 6-Core Processor ($295.00 @ PCCaseGear)
Motherboard: ASRock - AB350 Pro4 ATX AM4 Motherboard ($124.00 @ Umart)
Memory: G.Skill - Ripjaws V Series 16GB (2 x 8GB) DDR4-3200 Memory ($195.00 @ Umart)
Storage: Crucial - MX300 275GB M.2-2280 Solid State Drive ($135.00 @ Umart)
Storage: Seagate - BarraCuda 1TB 3.5" 7200RPM Internal Hard Drive ($64.00 @ Shopping Express)
Video Card: Gigabyte - GeForce GTX 1080 8GB WINDFORCE OC 8G Video Card ($699.00 @ Umart)
Case: Phanteks - ECLIPSE P400S TEMPERED GLASS ATX Mid Tower Case ($129.00 @ PCCaseGear)
Power Supply: Antec - High Current Gamer 620W 80+ Bronze Certified Semi-Modular ATX Power Supply ($111.00 @ IJK)
Operating System: Microsoft - Windows 10 Home OEM 64-bit
Total: $1752.00
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-07-03 11:06 AEST+1000

Please explain this issue, and whether or not it really matters.

 

[USAFRet]

If you use an m.2 SATA drive in the m.2_2 slot, the SATA 3 port on the motherboard will be disabled.
http://www.asrock.com/mb/AMD/AB350%20Pro4/#Specification

Since you probably won't be using the SATA_3 port on the motherboard...nothing to worry about.
(until a couple years from now when you add drives to this system)

 

[atljsf]

that is not an issue, is a reality, a condition of operation with m.2 devices in this case

it means that if you use the m.2 slot other components will have less pci express lanes to communicate with the cpu, so they will not work at full speed, or some will not work

if you are not going to use m.2, then the lanes will be used by the sata ports, or if you use the m.2 your sata devices will get less than they would like to get, so a port is disabled

on this case if the mainboard has 6 sata ports and you use the m.2 with the mx300, one of the 5 sata ports will end disabled, so you get only 5 sata ports usable, you are going to use 1 with the hard disk, remains 4 available and usable, so all is covered there