Every multi-port NAS plan ends at two physical things: a cable and a switch port. They are the cheapest parts of the build and the source of most of its failures. This page is the ten-minute physical audit to run before blaming DSM.
Software gets the suspicion; copper does the crime. A second LAN card doubles the number of cables, plugs and ports involved in your NAS — and each one can quietly downgrade the whole setup. Nothing on this page costs real money. Everything on it costs speed when ignored.
☐ Both cables are at least Cat5e — no flat, no-name specials
☐ Each cable clicks in at both ends and shows a gigabit link
☐ Both NAS ports land on the same switch (for LACP modes)
☐ Every switch port in the plan is the same speed
☐ Both ends of every cable are labelled with its port number
Cat5e carries gigabit perfectly well, and 2.5 GbE over normal home and office distances too. Cat6 and 6a earn their keep on 10 GbE runs and long permanent wiring. Category is rarely the problem.
Quality is. The real enemies are thin flat cables, no-name copper-clad aluminium (CCA) sold as copper, and runs that have been kinked, stapled or crushed under furniture. A cable like that can pass files at 100 Mbps for years and never confess it cannot carry gigabit on all four pairs.
Gigabit Ethernet uses all eight wires. A plug crimped with one bad pair still links up — politely, at 100 Mbps, or at gigabit with a stream of errors underneath. The lights look fine either way, which is why cables get away with it.
So when one leg of a bond is slow, the cable and its plugs are suspect number one, ahead of every setting in DSM. Swapping in a known-good patch lead takes two minutes and returns a verdict no amount of menu-reading can give you.
Aggregation members should be same-speed ports on the same switch. Scattering the legs — one into the router, one into a spare switch, one into whatever socket was free — builds a bond out of three different networks' worth of behaviour and then asks DSM to make it coherent.
Keep two adjacent switch ports free when you plan the build, and write down which physical port corresponds to which DSM interface and which MAC address. It is the same discipline the video applies to MAC addresses, applied to sockets: identity first, cables second.
Put a tape flag with the port number on both ends of every cable, and keep a one-line map somewhere you will actually find it: MAC address, DSM interface name, switch port, IP address, job.
This looks like bureaucracy until the first fault. With the map, "the NAS got slower" becomes a five-minute check of two known cables. Without it, it becomes an afternoon of pulling plugs behind a cabinet and hoping.
A cable that failed at gigabit does not become the printer cable. It becomes next month's mystery fault, on a different device, in a different room, with no memory of its history.
Cut it or bin it. A certified replacement patch lead costs less than one hour of troubleshooting, and a small stock of known-good cables is the cheapest diagnostic instrument a network can own.
Do the five-box physical check first, then watch the video and finish the build on a foundation you have verified.
▶️ Watch Full VideoYes. Each leg of a gigabit bond is one gigabit link, and Cat5e is a gigabit cable at any normal home or office length. Category matters when a single leg must carry 10 Gbps, not when two legs carry one gigabit each.
Usually the plug, not the cable category: one damaged pair or a tired socket. Swap the cable end for end, then swap the cable itself. If the fault follows the cable, replace it. If it stays with the port, inspect the socket pins.
Ethernet allows 100 metres per run including patch leads, and home and office runs are rarely anywhere near it. Problems at short distances are almost always termination quality, not length.