M.2 PCIe Bandwidth question

[Backskater]

hey all

so I'm getting a new pc, and reading into the motherboard/hard drive specifications and learning more about PCIe lanes, I came upon a question I couldn't find a clear answer to

the motherboard is the gigabyte z370 gaming 5, which has:

1 PCIe x16 (will be occupied by the GPU)
1 PCIe x16 (runs at x8)
1 PCIe x16 (runs at x4)
1 PCIe x1

and 3 m.2 slots, two of which are SATA and/or PCIe x4/x2 compatible, and one that shares bandwidth with the PCIe x4 slot

so I have my eye on an intel optane ssd, and one samsung 970 EVO ssd (as well as 2 hdd's for storage)

I would need to use 2 m.2 slots, but I'm not sure which ones, the two SATA/PCIe x4 do not share bandwidth with the PCIe slots, does this mean they'll just use the slower SATA slots? and if so, what would be the best way to place them? the optane or normal m.2 ssd in the PCIe x4 slot?

thank you in advance for your help

 

[raisonjohn]

..."the two SATA/PCIe x4 do not share bandwidth with the PCIe slots, does this mean they'll just use the slower SATA slots?"

Only one of the two aforementioned SATA/PCIe x4 slots, i.e., the one labelled M2A (middle M.2 slot), will disable a SATA port (SATA3_0 port) on the *SPECIFIC CONDITION* that such M.2 slot is used in SATA-mode, i.e., a SATA-based M.2 SSD is plugged in it. However, if the M2A slot is used in PCIe-mode, i.e., plugged with a PCIe-based M.2 SSD, then, it will run in PCIe speeds and will not disable any SATA ports.

The available Intel Optane M.2 SSD models (800p series) are PCIe-based but run only in PCIe3.0 x2 speeds. This means that when you plug it in any of the M.2 slots in the Gigabyte Z370 Gaming 5 mobo (since all the M.2 slots in that mobo support full PCIe3.0 x4 M.2 speeds), it will only achieve a max. PCIe3.0 x2 (the Intel Optane module being the limiting factor). Note that there are other Intel (non-Optane) M.2 SSD models that are SATA-based running in SATA3.0 6Gbps (e.g., 540s series) and models that are PCIe-based running in full PCIe3.0 x4 max. speeds (e.g., 600p and 660p series).

The second of the two aforementioned SATA/PCIe x4 slots, i.e., the one labelled M2M (topmost M.2 slot), when populated, will *ALWAYS* disable two SATA ports (SATA3_4 and SATA3_5 ports), whether the M.2 slot is being used in SATA-mode or PCIe-mode (i.e., whatever M.2 module/interface you use).

The last M.2 slot, i.e., the one labelled M2P (bottom-most M.2 slot), only runs in PCIe-mode (i.e., it cannot support SATA-based M.2 modules). As you have mentioned, this specific M.2 slot shares bandwidth with a PCIe x16 slot (the bottom-most running at x4 only). Using this M.2 slot will not fully disable the PCIe x16 slot, but, will take away lanes to run that PCIe x16 slot in x2 speeds only.

All these three M.2 slots are all controlled via the Z370 chipset (not the CPU).

"what would be the best way to place them? the optane or normal m.2 ssd in the PCIe x4 slot?"

You have several options to choose from:

Option 1:
M2M - [Intel Optane SSD, PCIe3.0 x2] --> disables SATA3_4 and SATA3_5
M2A - [Samsung 970 EVO, PCIe3.0 x4] --> does not disable any ports
M2P - none
SATA ports remaining = 4 / 6

Option 2:
M2M - none
M2A - [Intel Optane SSD, PCIe3.0 x2] --> does not disable any ports
M2P - [Samsung 970 EVO, PCIe3.0 x4] --> makes the bottom PCIe3.0 x16 slot run in x2 speeds (instead of x4)
SATA ports remaining = 6 / 6

Option 3:
M2M - [Samsung 970 EVO, PCIe3.0 x4] --> disables SATA3_4 and SATA3_5
M2A - none
M2P - [Intel Optane SSD, PCIe3.0 x2] --> makes the bottom PCIe3.0 x16 slot run in x2 speeds (instead of x4)
SATA ports remaining = 4 / 6

*interchanging the Intel Optane SSD and the Samsung 970 EVO in their respective slots in the above options will yield same result.

So, if you need all 6x SATA ports in your motherboard, then choose Option 2. If you need the bottom PCIe3.0 x16 slot in its full x4 speed, then choose Option 1. If 4x SATA ports is more than enough and you will not be using the bottom PCIe3.0 x16 in full x4 speed, then you can choose any of the above options.

 

[Backskater]

that's the answer I was looking for and more

detailed and clear, thank you

 

[raisonjohn]

You're welcome. Glad to be of help.

 

[mr.barnadib]

..."the two SATA/PCIe x4 do not share bandwidth with the PCIe slots, does this mean they'll just use the slower SATA slots?"

Only one of the two aforementioned SATA/PCIe x4 slots, i.e., the one labelled M2A (middle M.2 slot), will disable a SATA port (SATA3_0 port) on the *SPECIFIC CONDITION* that such M.2 slot is used in SATA-mode, i.e., a SATA-based M.2 SSD is plugged in it. However, if the M2A slot is used in PCIe-mode, i.e., plugged with a PCIe-based M.2 SSD, then, it will run in PCIe speeds and will not disable any SATA ports.

The available Intel Optane M.2 SSD models (800p series) are PCIe-based but run only in PCIe3.0 x2 speeds. This means that when you plug it in any of the M.2 slots in the Gigabyte Z370 Gaming 5 mobo (since all the M.2 slots in that mobo support full PCIe3.0 x4 M.2 speeds), it will only achieve a max. PCIe3.0 x2 (the Intel Optane module being the limiting factor). Note that there are other Intel (non-Optane) M.2 SSD models that are SATA-based running in SATA3.0 6Gbps (e.g., 540s series) and models that are PCIe-based running in full PCIe3.0 x4 max. speeds (e.g., 600p and 660p series).

The second of the two aforementioned SATA/PCIe x4 slots, i.e., the one labelled M2M (topmost M.2 slot), when populated, will *ALWAYS* disable two SATA ports (SATA3_4 and SATA3_5 ports), whether the M.2 slot is being used in SATA-mode or PCIe-mode (i.e., whatever M.2 module/interface you use).

The last M.2 slot, i.e., the one labelled M2P (bottom-most M.2 slot), only runs in PCIe-mode (i.e., it cannot support SATA-based M.2 modules). As you have mentioned, this specific M.2 slot shares bandwidth with a PCIe x16 slot (the bottom-most running at x4 only). Using this M.2 slot will not fully disable the PCIe x16 slot, but, will take away lanes to run that PCIe x16 slot in x2 speeds only.

All these three M.2 slots are all controlled via the Z370 chipset (not the CPU).

"what would be the best way to place them? the optane or normal m.2 ssd in the PCIe x4 slot?"

You have several options to choose from:

Option 1:
M2M - [Intel Optane SSD, PCIe3.0 x2] --> disables SATA3_4 and SATA3_5
M2A - [Samsung 970 EVO, PCIe3.0 x4] --> does not disable any ports
M2P - none
SATA ports remaining = 4 / 6

Option 2:
M2M - none
M2A - [Intel Optane SSD, PCIe3.0 x2] --> does not disable any ports
M2P - [Samsung 970 EVO, PCIe3.0 x4] --> makes the bottom PCIe3.0 x16 slot run in x2 speeds (instead of x4)
SATA ports remaining = 6 / 6

Option 3:
M2M - [Samsung 970 EVO, PCIe3.0 x4] --> disables SATA3_4 and SATA3_5
M2A - none
M2P - [Intel Optane SSD, PCIe3.0 x2] --> makes the bottom PCIe3.0 x16 slot run in x2 speeds (instead of x4)
SATA ports remaining = 4 / 6

*interchanging the Intel Optane SSD and the Samsung 970 EVO in their respective slots in the above options will yield same result.

So, if you need all 6x SATA ports in your motherboard, then choose Option 2. If you need the bottom PCIe3.0 x16 slot in its full x4 speed, then choose Option 1. If 4x SATA ports is more than enough and you will not be using the bottom PCIe3.0 x16 in full x4 speed, then you can choose any of the above options.

is those options also aplied to gigabyte aorus master z390 motherboard?

 

[mr.barnadib]

..."the two SATA/PCIe x4 do not share bandwidth with the PCIe slots, does this mean they'll just use the slower SATA slots?"

Only one of the two aforementioned SATA/PCIe x4 slots, i.e., the one labelled M2A (middle M.2 slot), will disable a SATA port (SATA3_0 port) on the *SPECIFIC CONDITION* that such M.2 slot is used in SATA-mode, i.e., a SATA-based M.2 SSD is plugged in it. However, if the M2A slot is used in PCIe-mode, i.e., plugged with a PCIe-based M.2 SSD, then, it will run in PCIe speeds and will not disable any SATA ports.

The available Intel Optane M.2 SSD models (800p series) are PCIe-based but run only in PCIe3.0 x2 speeds. This means that when you plug it in any of the M.2 slots in the Gigabyte Z370 Gaming 5 mobo (since all the M.2 slots in that mobo support full PCIe3.0 x4 M.2 speeds), it will only achieve a max. PCIe3.0 x2 (the Intel Optane module being the limiting factor). Note that there are other Intel (non-Optane) M.2 SSD models that are SATA-based running in SATA3.0 6Gbps (e.g., 540s series) and models that are PCIe-based running in full PCIe3.0 x4 max. speeds (e.g., 600p and 660p series).

The second of the two aforementioned SATA/PCIe x4 slots, i.e., the one labelled M2M (topmost M.2 slot), when populated, will *ALWAYS* disable two SATA ports (SATA3_4 and SATA3_5 ports), whether the M.2 slot is being used in SATA-mode or PCIe-mode (i.e., whatever M.2 module/interface you use).

The last M.2 slot, i.e., the one labelled M2P (bottom-most M.2 slot), only runs in PCIe-mode (i.e., it cannot support SATA-based M.2 modules). As you have mentioned, this specific M.2 slot shares bandwidth with a PCIe x16 slot (the bottom-most running at x4 only). Using this M.2 slot will not fully disable the PCIe x16 slot, but, will take away lanes to run that PCIe x16 slot in x2 speeds only.

All these three M.2 slots are all controlled via the Z370 chipset (not the CPU).

"what would be the best way to place them? the optane or normal m.2 ssd in the PCIe x4 slot?"

You have several options to choose from:

Option 1:
M2M - [Intel Optane SSD, PCIe3.0 x2] --> disables SATA3_4 and SATA3_5
M2A - [Samsung 970 EVO, PCIe3.0 x4] --> does not disable any ports
M2P - none
SATA ports remaining = 4 / 6

Option 2:
M2M - none
M2A - [Intel Optane SSD, PCIe3.0 x2] --> does not disable any ports
M2P - [Samsung 970 EVO, PCIe3.0 x4] --> makes the bottom PCIe3.0 x16 slot run in x2 speeds (instead of x4)
SATA ports remaining = 6 / 6

Option 3:
M2M - [Samsung 970 EVO, PCIe3.0 x4] --> disables SATA3_4 and SATA3_5
M2A - none
M2P - [Intel Optane SSD, PCIe3.0 x2] --> makes the bottom PCIe3.0 x16 slot run in x2 speeds (instead of x4)
SATA ports remaining = 4 / 6

*interchanging the Intel Optane SSD and the Samsung 970 EVO in their respective slots in the above options will yield same result.

So, if you need all 6x SATA ports in your motherboard, then choose Option 2. If you need the bottom PCIe3.0 x16 slot in its full x4 speed, then choose Option 1. If 4x SATA ports is more than enough and you will not be using the bottom PCIe3.0 x16 in full x4 speed, then you can choose any of the above options.

is those options also applied to gigabyte aorus master z390 motherboards?

 

[mr.barnadib]

is those options also applied to gigabyte aorus master z390 motherboards?

 

[rbassett15]

You're welcome. Glad to be of help.

can you please explain how you did to him but if we were to use all 3 m.2 slots please?