MCX312B-XCCT Mellanox ConnectX-3 Pro 10GbE Adapter Guide
The MCX312B-XCCT is a Mellanox ConnectX-3 Pro dual-port 10 gigabit network adapter with SFP+ ports. It is a widely deployed card, and there is one thing about it worth establishing before you order.
Check driver support for your operating system first
The most important consideration with this card, and the one that catches people.
ConnectX-3 is an established generation, and support for older adapter generations is progressively withdrawn from current operating systems and hypervisors. A card that works perfectly on one version may not be supported on the next.
Two consequences.
Check the specific version you intend to run, not the one currently installed. An upgrade planned for later can strand the card.
Check the hypervisor compatibility list if this is going in a virtualisation host, since those lists are stricter and drop older devices sooner. Our compatibility guide covers checking against the version you are moving to.
This is not a reason to avoid the card. It is a reason to confirm before ordering rather than after, and it is a genuine consideration on any adapter of this generation.
Transceivers are not included
The most common omission in an order for a card like this.
SFP+ ports are cages. They ship empty, and the transceivers or direct-attach cables are separate parts.
Three things to establish.
What your switch expects — fibre type and distance, or direct-attach copper for short runs within a rack.
Vendor coding. Transceivers carry coding, and some switches accept only their own. The card end is generally more permissive than the switch end. Our transceiver guide covers this properly.
Matching at both ends. The transceiver at each end of a fibre link must match in type and wavelength.
For short in-rack connections, direct-attach copper cables are frequently cheaper and simpler than optics plus fibre — worth considering before buying transceivers by default.
PCIe requirements
Two checks.
Sufficient lanes. A dual-port 10 gigabit adapter needs meaningful bandwidth, and physical slot size is not the same as electrical width. A card in an under-wired slot works at reduced throughput with nothing reported as a fault — our PCIe guide covers this and notes that on dual-socket machines some slots are dead with only one processor fitted.
Bracket height. 1U servers generally take low-profile cards only, and a card supplied with only a full-height bracket needs the correct low-profile one sourced separately. Check what ships in the box.
Where the server has a dedicated network slot rather than standard PCIe, a standard card will not fit it — our network adapter guide covers the distinction.
Where 10 gigabit is worth having
Worth checking rather than assuming, since the upgrade frequently changes nothing.
It helps where the network is genuinely the bottleneck — storage traffic to a NAS or SAN, backup windows constrained by transfer time, virtualisation hosts carrying many guests' traffic on shared links, and any workload moving large volumes between machines.
It helps less where the constraint is elsewhere. A backup that runs slowly because the storage behind it is slow does not improve with a faster network, and our performance guide covers establishing where the limit actually is.
The other requirement people miss: the switch has to support it too. A 10 gigabit adapter connected to a gigabit switch port runs at gigabit, which is correct behaviour and a regular surprise. Check negotiated speed after installation — our network monitoring guide covers why that check is worth doing routinely.
Redundancy
Two ports on one card protect against a cable or switch port failing. They do not protect against the card failing.
Where the machine's availability matters, two separate cards connected to two different switches is what actually gives resilience. Whether that is warranted depends on what the machine does, and it is worth deciding deliberately rather than assuming two ports equals redundancy.
Before you order
Your server model and generation, and how many processors are fitted. What free slots exist, their electrical width and whether they are low-profile. What operating system or hypervisor version you will run — the one you are moving to, not the current one. What your switch expects at the other end. And whether you need transceivers or direct-attach cables, and for what distance.
Common questions
Will this card work with my operating system?
Check the specific version you intend to run rather than the one installed. Support for older adapter generations is progressively withdrawn from current operating systems and hypervisors, and hypervisor lists drop older devices sooner.
Does it come with transceivers?
No. SFP+ ports are cages and ship empty — transceivers or direct-attach cables are separate parts. For short in-rack connections, direct-attach copper is frequently cheaper and simpler than optics plus fibre.
Why is my link only running at 1 gigabit?
Most likely the switch port. A 10 gigabit adapter connected to a gigabit port runs at gigabit, which is correct behaviour. It can also be insufficient PCIe lanes, since physical slot size is not the same as electrical width.
Will 10 gigabit speed up my backups?
Only if the network is the bottleneck. A backup that runs slowly because the storage behind it is slow does not improve with a faster network — measure where the limit actually is before buying.
Do two ports give me redundancy?
Against a cable or switch port failing, yes. Against the card failing, no. Two separate cards connected to two different switches is what actually gives resilience.
Send us your server model, the operating system version you will run and what your switch expects, and we will confirm the card and transceivers together.
