Synology Load Balancing & Link Aggregation Overview

by Ray Newbery in ,


Several Synology NAS devices have multiple network (NIC) ports and can bond the ports together to enhance performance. With DSM 5.2 Synology supports four ways of bonding the ports together:

  1. Adaptive Load Balancing: This is the easiest to set up and doesn’t require any special hardware. Any network switch can be used, even consumer level switches or the ports that may be built in to your network router. You can also hook each port up to a different switch to provide some redundancy.
  2. IEEE 802.3ad Dynamic Link Aggregation: This is more complex[1] and more expensive to set up. You’ll need a switch that supports 802.3ad LACP. While there may be an exception, I haven’t seen consumer level switches that support this. Unless you can find one used expect to pay over $100 for a switch.
  3. Balance XOR: This is the older standard 802.3ad draft v1 and is called Static Link Aggregation. This is the most complex to set up, at least potentially. You must configure both DSM and the switch. What makes it potentially more complex is that there is less error detection and reporting so a configuration error may go unnoticed. Also, if a switch port or cable fails the DSM or client software may not fail over and will continue to try and use the bad connection. LACP also does a more efficient job of balancing the connections across the ports. If at all possible use LACP instead of static configuration.
  4. Active/Standby: This only provides fault-tolerance. No special hardware is needed and different switches can be used.

So, which should be used? Well, it depends. (Don’t you hate that answer?)

Because Adaptive Load Balancing (option 1) is inexpensive (assuming you already have a Synology NAS that supports it) to implement so there’s little reason not to do it. Option 4 (Active/Standby) doesn’t provide any performance improvement so I’d generally recommend going with Adaptive Load Balancing (option 1) instead. These are also the easiest options to implement.

If you’re a home or small business Synology user then I’d recommend using Adaptive Load Balancing rather than incurring the time and expense to set up Link Aggregation.

What if you are able to buy hardware (or already have it)?

For load balancing and link aggregation there’s often no performance benefit if all you’ve got is one other PC or device communicating with the Synology NAS. There’s little benefit to spend the money for a switch that supports 802.3ad if you’ve only got one or two client computers. So if you only one or two computers, save the money unless you really heavily use those PCs. In theory, Adaptive Load Balancing (option 1) and LACP (option 2) should perform about the same in most home and small business environments[2].

If you do want to do link aggregation, rather than just Adaptive Load Balancing or failover, you’ll need a switch that supports 802.3ad LACP. (Only go for Balance XOR if you can get a used switch super cheap and just want to try it out[3].) I like, and use, the TP-LINK TL-SG2216 in my home & lab. It’s main attraction is the price but it is also easy to configure and contains a bevy of features, most of which go unused.

Also, for both Static and Dynamic link aggregation the same physical switch must be used for all ports[4].

Which Synology NASs have multiple network connections?

If you’re shopping for a Synology NAS that supports network bonding there’s no 100% reliable way to tell just from the model number. But there are some rules that make sense based on who the model is targeted for. If a model has multiple NICs then it does support network bonding so you can check the specs on any model. Currently, all “+” models have two or more network ports so support bonding as do all the rack mountable unit (“RS” as the model prefix). The low-end “J” models only have one network port, so none support bonding. As for the rest, some do and some don’t.

Why do I use Link Aggregation?

The short answer is “Because Adaptive Load Balancing is new with DSM 5.2 and didn’t exist when I set up link aggregation.” I plan to switch to Adaptive Load Balancing in the near future so I can compare it. If I was deciding today I’d start with load balancing and would fully expect it to meet my needs.

I did set it up for the following benefits which I would also expect from Adaptive Load Balancing:
1. I power up a NAS every night to do backups. While the NAS is powered up all my computers and other Synology NASs do their backups to this NAS. Since there are multiple connections the backups happen much faster than if there was only a regular network connection.
2. I sometimes stream video to my TV while using my computer to run a virtual machine loaded from the NAS or doing some heavy file copies. There was a noticeable improvement in performance when I implemented link aggregation.
3. Moving files around, from computer to NAS or NAS to NAS has also been faster

The addition of Adaptive Load Balancing in DSM 5.2 really brought enhanced performance to budget conscience homes and small businesses. It’s not longer necessary to buy special hardware. If you have the hardware or have more complex networking needs then Link Aggregation is still available and being enhanced by Synology.


  1. By complex I mean you’ll have to configure both DSM and the switch hardware.  ↩

  2. Adaptive Load Balancing (ALB) is new, hence the “in theory”. I haven’t used ALB yet.  ↩

  3. The problem with this is that what you save in money you may more than make up in time in order to get things working.  ↩

  4. Multiple switches can be used but must be stackable and the ports must be configured to support link aggregation across the different hardware switches making it look like one switch. Generally speaking, homes and small businesses will not have or need this complex of a network configuration.  ↩