M.2 vs SATA

[EPPHO]

M.2 SSD with same write/read speeds has same actual "real life" performance as SATA SSD does, or not?

[Sakkura]

Probably. Depends what you're comparing.

 

Also bear in mind many M.2 SSDs actually are SATA SSDs, just not in 2.5" form.

[Oshino Shinobu]

M.2 is just an interface. M.2 SSDs can be SATA SSDs. 

 

In terms of M.2 SATA/AHCI drives vs normal SATA drives, the performance should be around the same, but there is variation among drives, just as there is among regular 2.5" SATA SSDs. 

[79wjd]

Even the fastest NVME M.2 drive will have the same "real life" feel (not performance) for most users as its the latency that makes a big difference. 

[Spork829]

As others have said an M.2 can run off of anything, including SATA, making it no faster than a normal SATA drive. But if it's PCIe/NVME as many are these days, there's a bit of a performance increase. However for day-to-day normal user stuff, it's not worth the extra cost IMO.

[Princess Luna]

M.2 is just a fancy new form, which can be useful in dead tight small mini itx builds

 

NVMe is cool and all, like PCI-e SSDs... they are better but the average user won't gain any benefit at all from it, and since it costs so much more than a normal SATA 3 SSD I never really advise those.

[EPPHO]

4 minutes ago, Sakkura said:

Probably. Depends what you're comparing.

 

Also bear in mind many M.2 SSDs actually are SATA SSDs, just not in 2.5" form.

 

3 minutes ago, Oshino Shinobu said:

M.2 is just an interface. M.2 SSDs can be SATA SSDs. 

 

In terms of M.2 SATA/AHCI drives vs normal SATA drives, the performance should be around the same, but there is variation among drives, just as there is among regular 2.5" SATA SSDs. 

 

3 minutes ago, djdwosk97 said:

Even the fastest NVME M.2 drive will have the same "real life" feel (not performance) for most users. 

 

1 minute ago, Spork829 said:

As others have said an M.2 can run off of anything, including SATA, making it no faster than a normal SATA drive. But if it's PCIe/NVME as many are these days, there's a bit of a performance increase. However for day-to-day normal user stuff, it's not worth the extra cost IMO.

 

1 minute ago, Princess Cadence said:

M.2 is just a fancy new form, which can be useful in dead tight small mini itx builds

 

NVMe is cool and all, like PCI-e SSDs... they are better but the average user won't gain any benefit at all from it, and since it costs so much more than a normal SATA 3 SSD I never really advise those.

Thanks for fast response  

[jools]

go sata sdd, don't choke pci lanes

[79wjd]

10 minutes ago, jools said:

go sata sdd, don't choke pci lanes

The PCIE lanes go over the chipset, so it doesn't actually matter. But regardless, x8 for a GPU isn't going to limit it anyway. Also, an M.2 Sata SSD doesn't use PCIE lanes. 

[mariushm]

They don't always go to the chipset.

Ryzen cpu has 4 pci-e v3.0 lanes which can be used for a M.2 connector, or they can be split in a pci-e v3.0 x2 link for m.2 connector and 2 x1 links for other things, or all four can be used for other things.

 

in a very simplified way...

 

SATA is 6gbps with a 10:8 encoding (for every 10 bits, 8 bits are actual content, the other 2 are error correction information), so it can transfer in either direction 4.8 gbps or 600.000.000 bytes  or 600 MB / 572 MiB

 

M.2 is a connector that has a sata connection AND a pci-e connection with maximum 4 lanes (x4). These lanes can be v2.0 or v3.0 so we have either ~ 500 MB/s for each lane, or around 980 MB/s for each lane ( because pci-e v2.0 works with 10:8 encoding, while pci-e v3.0 works with 130/128 encoding)

 

The manufacturer of the motherboard can connect all four lanes to the m.2 connector, or they can connect only two , or they can connect none at all which means only m.2 drives which support SATA will work in that m.2 connector.

Also, manufacturers can wire four pci-e lanes to the connector, but then allow user to go in BIOS and limit the number of pci-e lanes to 2 in order to enable a couple of pci-e x1 slots (for add-on cards) or maybe to enable an additional onboard sata controller that needs one pci-e lane.

 

Now the m.2 ssd itself :

 

Each SSD uses a controller, a chip.

Very cheap m.2 SSDs may have a value oriented controller that only has the sata interface, so that m.2 SSD will only talk through the SATA connection in the m.2 connect so you'll only get 600 MB/s in both directions.

Better ssd controllers may have both SATA (for backwards compatibility with connectors that have only sata wired in them) and maybe a pci-e x1 or at best x2 - so you may get up to 500/980 MB/s (for x1)  or up to 1000 MB/s / 1960 MB/s

The best ssd controllers would have both SATA and up to four lanes of pci-e giving you up to 2000 MB/s (4x500) for pci-e v2 / ~ 3950 MB/s for pci-e v3

 

Then we have the differences in how the data is read and written to ssd drives.

 

SSD controllers achieve that speed by using channels, just like motherboards have dual channel ddr3/ddr4 or triple / quad channel ddr3/ddr4 - they read and write to multiple memory chips at the same time.

The most common configurations for ssd controllers are 4 channel and 7 8 (much later edit: noticed the typo) channel - in the past Intel had some controller that had 10 channels but i don't think there is anymore.

Due to the mechanical limitations (surface of the m.2 ssd), most  m.2 ssd's have controllers with maximum 4 channels and they use at most only 4 memory chips or if you're lucky they have 2 memory chips on each of the 4 memory channels.

The SATA ssd drives may or may not use more than 4 channels.

Most cheap controllers and TLC drives (i'd say majority of ssd drives 256GB or less) will use controllers with only 4 channels.  Higher capacity or higher end drives (and most MLC based SSD drives) will use controllers with 8 channels.

A higher number of channels means the SSD will have higher read and write speeds and it also means the SSD controller can move data around from memory chip to memory chip for wear leveling purposes, to extend the life of each memory chip, for more endurance. Flash memory chips have a limited number of erase cycles, so more memory channels and more memory chips can prolong the life of a SSD drive.

Regular SSD drives also have more room which would allow for adding a 128/256/512 MB DDR3 memory chip which helps with caching writes and reads, so again it reduces the number of erase cycles prolonging the life of a SSD.

Some SSD controllers have some amount of DDR memory basically put on top of the controller chip and then placed in a nice package, I think Samsung has some of those controllers with DDR memory hidden inside them, so separate memory chip would not be required.

 

Anyway.. the point is the bigger regular SSDs are more flexible, they allow for more channels, they allow for addition of caching memory, and because the pcb is in a case, if needed they can also use the case as a sort of heatsink to spread the heat from the chips.

 

You ARE limited by the maximum speed of the SATA connector (to 600 MB/s) but you may or may not get other benefits (higher speeds at bigger queue depths - when lots of files are requested at the same time - , endurance, bigger caching with extra ddr memory, higher warranty, cooler drive, more powerful controller with support for things like encryption, sometimes even added battery or capacitor bank inside to have enough energy to store everything to drive if power fails)

 

 

Edited May 5, 2017 by mariushm
8 channels , not 7 .. typo in text

[EPPHO]

On 5/4/2017 at 5:04 PM, mariushm said:

They don't always go to the chipset.

Ryzen cpu has 4 pci-e v3.0 lanes which can be used for a M.2 connector, or they can be split in a pci-e v3.0 x2 link for m.2 connector and 2 x1 links for other things, or all four can be used for other things.

 

in a very simplified way...

 

SATA is 6gbps with a 10:8 encoding (for every 10 bits, 8 bits are actual content, the other 2 are error correction information), so it can transfer in either direction 4.8 gbps or 600.000.000 bytes  or 600 MB / 572 MiB

 

M.2 is a connector that has a sata connection AND a pci-e connection with maximum 4 lanes (x4). These lanes can be v2.0 or v3.0 so we have either ~ 500 MB/s for each lane, or around 980 MB/s for each lane ( because pci-e v2.0 works with 10:8 encoding, while pci-e v3.0 works with 130/128 encoding)

 

The manufacturer of the motherboard can connect all four lanes to the m.2 connector, or they can connect only two , or they can connect none at all which means only m.2 drives which support SATA will work in that m.2 connector.

Also, manufacturers can wire four pci-e lanes to the connector, but then allow user to go in BIOS and limit the number of pci-e lanes to 2 in order to enable a couple of pci-e x1 slots (for add-on cards) or maybe to enable an additional onboard sata controller that needs one pci-e lane.

 

Now the m.2 ssd itself :

 

Each SSD uses a controller, a chip.

Very cheap m.2 SSDs may have a value oriented controller that only has the sata interface, so that m.2 SSD will only talk through the SATA connection in the m.2 connect so you'll only get 600 MB/s in both directions.

Better ssd controllers may have both SATA (for backwards compatibility with connectors that have only sata wired in them) and maybe a pci-e x1 or at best x2 - so you may get up to 500/980 MB/s (for x1)  or up to 1000 MB/s / 1960 MB/s

The best ssd controllers would have both SATA and up to four lanes of pci-e giving you up to 2000 MB/s (4x500) for pci-e v2 / ~ 3950 MB/s for pci-e v3

 

Then we have the differences in how the data is read and written to ssd drives.

 

SSD controllers achieve that speed by using channels, just like motherboards have dual channel ddr3/ddr4 or triple / quad channel ddr3/ddr4 - they read and write to multiple memory chips at the same time.

The most common configurations for ssd controllers are 4 channel and 7 channel - in the past Intel had some controller that had 10 channels but i don't think there is anymore.

Due to the mechanical limitations (surface of the m.2 ssd), most  m.2 ssd's have controllers with maximum 4 channels and they use at most only 4 memory chips or if you're lucky they have 2 memory chips on each of the 4 memory channels.

The SATA ssd drives may or may not use more than 4 channels.

Most cheap controllers and TLC drives (i'd say majority of ssd drives 256GB or less) will use controllers with only 4 channels.  Higher capacity or higher end drives (and most MLC based SSD drives) will use controllers with 8 channels.

A higher number of channels means the SSD will have higher read and write speeds and it also means the SSD controller can move data around from memory chip to memory chip for wear leveling purposes, to extend the life of each memory chip, for more endurance. Flash memory chips have a limited number of erase cycles, so more memory channels and more memory chips can prolong the life of a SSD drive.

Regular SSD drives also have more room which would allow for adding a 128/256/512 MB DDR3 memory chip which helps with caching writes and reads, so again it reduces the number of erase cycles prolonging the life of a SSD.

Some SSD controllers have some amount of DDR memory basically put on top of the controller chip and then placed in a nice package, I think Samsung has some of those controllers with DDR memory hidden inside them, so separate memory chip would not be required.

 

Anyway.. the point is the bigger regular SSDs are more flexible, they allow for more channels, they allow for addition of caching memory, and because the pcb is in a case, if needed they can also use the case as a sort of heatsink to spread the heat from the chips.

 

You ARE limited by the maximum speed of the SATA connector (to 600 MB/s) but you may or may not get other benefits (higher speeds at bigger queue depths - when lots of files are requested at the same time - , endurance, bigger caching with extra ddr memory, higher warranty, cooler drive, more powerful controller with support for things like encryption, sometimes even added battery or capacitor bank inside to have enough energy to store everything to drive if power fails)

 

 

I really appreciate your detailed answer! Thank you very much, now i know a lot more  about SSDs