Overview
Link Aggregation allows you to combine multiple 1GbE connections to get higher performance when multiple devices are connecting at the same time. One important thing to note: You cannot use Link Aggregation to gain a speed advantage when only one device is connected. Meaning you cannot use 4, 1GbE ports to get a faster than 125MB/s read/write on a large file transfer. Instead you can get up to 4 devices all getting the full 1GbE speeds.
This is the primary reason why most Synology models come with at least two ports. This not only allows for higher multi-user performance but also for failover. In the video above I demonstrate that with Dynamic Link-Aggregation, an link can go down in the middle of a transfer and the Synology will automatically redirect traffic to the remanning connections on the fly!
Configuration
To setup Dynamic Link Aggregation you need a switch that enables it. I am using a Netgear GS110EMX in this demonstration, but it is overkill for this purpose as it has two 10GbE ports. Instead I would recommend the Netgear GS308T which is part of their Smart Managed Pro line and supports Dynamic Link Aggregation.
Once you have your switch setup, it becomes incredibly easy to setup LCAP. First, connect multiple ethernet cables between your Synology and your Switch, and log in to DSM. Then go to Control panel -> Network -> Network Interface and select Create. This will bring up a menu allowing you to select which type of link aggregation / failover you would like.
For maximum performance, select Balance-TCP {Dynamic Link Aggregation}. Balance-TCP allows the Synology to automatically balance total traffic between the different connections. This will prevent a situation where one link is at capacity while the other once is idle, which can happen without active load balancing (Balence-SLB).
After selecting Balance-TCP, you will choose which network ports to combine into the link aggregation group. You can only select ports which are all the same speed, meaning you cannot combine a 10GbE port with a 1GbE port.
From here you can now setup Dynamic Link aggregation on your switch and you will be good to go! To see the results you will need two devices both running a speed test at the same time. Assuming your HDDs can take it – you should see more than 125MB/s read/write in total!
Caveats
People often think that link aggregation will be able to get them better than 125MB/s read/write with a single client. This is not true. With link aggregation, packets will only ever be sent down one connection at a time, meaning the 1GbE line cannot be broken.
SMB Multichannel is a protocol that does allow you to achieve higher speeds with a single client. However do not use this with Synology. Currently, SMB Multichannel is only in an experimental phase of SAMBA, the SMB server that Linux machines (including Synology) use. This means that data loss is entirely possible due to mis-matched packets.
