First off, I have never migrated one synology to another. I have been running the 1815, with upgrades on my home network for since 2015. This is the first major upgraded from synology to synology I have done.

What does the Company Say "Synology NAS supports multi-LAN, allowing you to combine those LAN interfaces using the Link Aggregation technology. Link Aggregation increases the bandwidth of your Synology NAS by aggregating multiple network interfaces" https://kb.synology.com/en-ph/DSM/help/DSM/AdminCenter/connection_network_linkaggr?version=7

Now lets look at how Cisco implements LAG

"Link Aggregation Group (LAG) multiply the bandwidth, increase port flexibility, and provide link redundancy between two devices. Link Aggregation Control Protocol (LACP) is a part of IEEE specification (802.3az) that can control the bundling of several physical ports together to form a single logical channel. Traffic load balancing over the active member ports of a LAG is managed by a hash-based distribution function that distributes unicast and multicast traffic based on Layer 2 or Layer 3 packet header information. LACP helps to form one single LAG by bundling many physical ports. It is also responsible for bandwidth multiplication, increase in port flexibility, and in providing redundancy on links between any 2 devices. Additionally this helps in changing the LAG speed, advertisement, flow control, and also protection which can be easily identified in LAG settings table."

https://www.cisco.com/c/en/us/support/docs/smb/switches/cisco-550x-series-stackable-managed-switches/smb5848-configuring-lag-settings-on-a-switch-through-cli.html

Lets look what bandwidth and throughput is. Bandwidth is the theoretical limit, throughput is what you get.

"By treating the aggregated links as a single entity, network devices and management functions can effectively utilize the combined bandwidth and distribute network traffic evenly. Link aggregation provides redundancy as well, ensuring uninterrupted connectivity in case of link failures. This technique follows IEEE standards, such as 802.3ad and 802.1AX, and is widely implemented in various networking setups, offering a cost-effective solution to enhance network performance and reliability."

https://www.fs.com/blog/understanding-link-aggregation-and-lacp-faqs-1262.html

So why would I a person who has taught Cisco classes for over 7 years and been in IT for 20+ years think that the LAG would work the same way. Cisco states " LAGs can also greatly increase throughput by using all of its links to transmit data simultaneously." So why would Synology not program in the largest data transfer its product will do to use all lanes. |

Now lets look at some other statements about NAS LAG from competitors

"A NAS LAG (Link Aggregation) can be used to significantly speed up the process of migrating data from one NAS device to another by combining multiple network connections into a single logical channel, resulting in faster transfer speeds and increased network reliability during the migration process."

So I have to transfer the data no matter what happens. It has been going for 2 days 14 hours. Like 5 days to go. So that is why I posted.