How to Use Two M.2 SSD?

SSDs have become the new norm when it comes to storage drives these days. They have almost replaced the old hard disk drives (HDD). While the HDDs still have their use, those who have had the taste of SSDs just cant have enough of them. Most PCs have a single M.2 SSDs slot, which begs the question “how to use two M.2 SSD on your PC?”

Fortunately, the process of having two SSDs on your PC is fairly simple. If you have multiple M.2 slots, on your motherboard, you can simply utilize them. If you do not have multiple M.2 slots on your motherboard then you will need to procure an M.2 Slot PCIe expansion card.

In the following text I will explain in detail whether can you use two M.2 SSDs on your PC and if so how.

A Primer on M.2 SSDs

It should be noted that there are two types of M.2 SSDs:

  1. NVMe 
  2. SATA

NVMe SSDs – The Golden Standard

samsung 980 pro
Samsung 980 Pro. PCIe 4.0 NVMe SSD

NVMe SSDs utilize the PCIe protocol. A typical NVMe M.2 slot utilizes 4 x PCIe lanes and its speed scales with the version of the PCIe protocol the M.2 slot conforms to.

So a Gen 3 (PCIe 3.0) M.2 NVMe SSD, such as the Samsung 970 Pro can typical reach a maximum of 3500 MB/s transfer rate . Whereas a Gen 4 (PCIe 4.0) M.2 NVMe SSD, such as the Samsung 980 Pro, can reach a maximum of about 6500 MB/s. 

Of course, whether you motherboard supports Gen 3 or Gen 4 SSDs depends upon your motherboard. 

NVMe SSDs are generally the golden standard. These are the SSDs that most modern desktop and laptops come with. However, you should always consult with the technical specs of your laptop or desktop in order to confirm what PCIe version the M.2 slot(s) your PC conforms. 

Also Read: Can You Use a PCIe 4.0 SSD On Your Existing Motherboard?

SATA SSDs – The Weaker M.2 SSDs

What are SATA Ports Used For
Samsung Evo 860 SATA SSD with M.2 form factor with B+M Key

M.2 SATA SSDs, use, well, the SATA protocol. SATA protocol is the generally intended for installing the slower Hard Disk Drives.

However, SATA also finds its use for SSDs. M.2 SATA SSDs run at the maximum transfer speed of the SATA protocol.

SATA 3 has a maximum theoretical transfer rate of 6 Gbps or 750 MB/s. In reality though, SATA 3 M.2 SSDs run at a maximum transfer rate of 550 MB/s.

This is many folds slower the than the NVMe SSDs.

Also Read: How to Tell if My M.2 Slot is NVMe or SATA?

Differentiating Between M.2 SATA and M.2 NVMe SSDs

Both SSDs should have label highlighting which protocol they use.

If they don’t then you can tell by the key notches which protocol they conform to:

m2 sata key
(Left) M.2 NVMe SSD uses the M Key; (Right) M.2 SATA SSD uses B+M Key. Source: atpinc.com
  • M Key is used by NVMe SSDs
  • B+M Key is used by SATA SSDs

Also Read: How to Add More M.2 SSD Slots?

So How to Use Two M.2 SSD?

Now that you understand the two protocols used for M.2 SSDs, you will be better equipped when when installing two M.2 drives to your PC or when procuring an expansion.

So there are two ways to add more M.2 SSDs to Your PC:

  1. Use the Built-in Motherboard M.2 Slots
  2. Use a PCIe Expansion Card

1. Adding 2 SSDs on the Motherboard’s Built In Slots

The simplest way to add 2 M.2 SSDs is to use the M.2 slots built onto the motherboard.

Almost all of the newer motherboards come with two or more M.2 SSDs slots.

You can tell how many M.2 slots you have by consulting the specsheet. Take for instance the MSI MEG B550 motherboard. This motherboard has a whopping 4 x M.2 SSDs slots:

how many M.2 slots do motherboards have
M.2 slots on MSI MEG B550 Unify. This motherboard has 4 x M.2 slots. Source: MSI

Of course this is an overkill, but a majority of the newer motherboards generally do feature multiple SSDs slots.

You can read a comprehensive article on this topic here: How Many M.2 Slots Do Motherboards Have?

Beware: Not All M.2 Slots are The Same!

You should take note of the fact that not all M.2 slots are the same.

Recall from earlier that a typical NVMe M.2 slot uses 4 x PCIe lanes. Meaning, in order for your SSD to work at full performance level, it will need 4 x PCIe lanes.

On some motherboards, however, the M.2 slot may only connect to 2 x PCIe lanes. Meaning, the connected NVMe SSD will only perform at half its rated performance!

Take for example the ASUS STRIX X470-F Gaming. This motherboard offers 2 x M.2 slot but with different lane counts. The second M.2 slot only connects to 2 PCIe lanes.

ASUS X470-F motherboard chipset Specifications 3

Read in Detail: How Many PCIe Lanes Does M.2 Slot?

2. Adding M.2 SSDs Using an Expansion Card

If your motherboard does not have two M.2 slots, then you will need to procure an M.2 expansion card in order to add more slots.

An M.2 expansion card is a PCIe device that connects to the PCIe expansion slots on the motherboard.

NVMe expansion card
An M.2 PCIe expansion card for adding. Slot for one NVMe SSD. Uses are 4 lane connector
Can PCIe X1 Card Fit in X4 Slot
Image: Different connector sizes of PCIe expansion card. The larger the connector, the more lanes the PCie expansion card uses. Image Source: howtogeek.com

Again there are multiple caveats and specifications you need to understand in order to buy the right M.2 PCIe expansion card:

NVMe M.2 Expansion Cards Have Different Sized Connectors

The size of the connector on an M.2 expansion card depends upon how many M.2 slots it has.

Again, recall that an M.2 slot intended for an NVMe SSD requires 4 x PCIe lanes.

Hence when it comes NVMe SSDs, the following are sizes you can find in relation to the number of slots they have.

  • 1 x M.2 NVMe SSD Slot – x4 connector
  • 2 x M.2 NVMe SSD Slot – x8 connector
  • 4 x M.2 NVMe SSD Slot – x16 connectors

The biggest card you can find is an x16 card with 4 x NVMe slots.

How to Use Two M.2 SSD
Asus Hyper M.2 Expansion card. 4 x M.2 NVMe Slots with x16 connector

SATA M.2 Expansion Cards Require Fewer PCIe Lanes

A SATA M.2 SSD does NOT require 4 x PCIE lanes. Since it is a slow interface, even two PCIe lanes can suffice for one SATA M.2 Slot.

Take for instance the following M.2 SATA SSD expansion card. It has an x4 connector, yet offers 2 x M.2 slots.

M.2 SATA expansion card
M.2 SATA SSD Expansion Card

The card above can also be used for NVMe SSDs, however, an NVMe SSD installed in any of these slots would only operate at half its overall capacity – since each slot connectors to only 2 lanes and NVMe SSDs ideally require 4 each.

As such, an expansion card such as the one above is ideal of SATA SSDs but NOT for NVMe SSDs.

Also Read: Do You Need an HDD and SSD Both?

You Need to Have a Free PCIe Expansion Slot

It goes without saying that in order to install an M.2 expansion card, you need to have a free PCIe slot on the motherboard for it.

So if you have an M.2 expansion card with x4 connector, you will need an x4 PCIe slot. If you have an x16 card, then you will need a slot with x16 lanes.

how to tell if pcie slot is bad w
Note the bottom x16 slot actually only has 4 lanes.

You will need to refer to the motherboard’s specsheet in order to figure out how many PCIe lanes each slot offers.

Often times what may seem like a full x16 slot may only in reality have x4, or x8 PCIe lanes.

Take for instance the motherboard above, if you were to install an x8 expansion card (2 x NVMe Slots) or an x16 expansion card (4 x NVMe M.2 Slots) on the bottom x16 slot, then the card will naturally not work since the bottom x16 slot is actually only connected to 4 x PCIe lanes. 

Read more about PCIe Lanes and Slots

Final Words

I talked comprehensively about how to use two M.2 SSDs here. Basically, first you need to understand a bit about SSDs and jargon around it in order to install and use two M.2 SSDs.

One of the first steps in using 2 x M.2 SSDs is read your motherboard specsheet. Among many other things, the motherboard specsheet can tell you

  • How many M.2 slots you have
  • Which PCIe version the M.2 slots conform to
  • Whether they support NVMe, SATA or Both SSDs
  • How many lanes a slot connects
  • Whether the slot shares its lanes with another PCIe slot.
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Author:

Atif Qazi
Atif Qazi is the founder of PCGuide101. He is a digital nomad who loves everything PC. He is a PC builder, tech enthusiast, engineer, and a lover of single player lore-rich RPG games.

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