It is the cache that gets populated for a WAN accelerator.  See here - Manual Population of Global Cache - Veeam Cookbook

Also, in the Help Docs here - Manually Populating Global Cache - User Guide for VMware vSphere (veeam.com)

Seeding uses Backups already at a remote site and Mapping uses full VM copies already at a remote site. If you have either one of those, especially for your 13TB VM, then by all means yes....use those for your initial BCJ sync/run. 

So,

Just to clarify it to me:

• I need to populate the cache with right click > populate cache on the source side for WAN Accelerator
• Where our backups reside on the Primary Site I need to populate cache to the source WAN Accelerator
• I don’t need to do anything for the Target WAN Accelerator, it will populate it when Backup Copy Jobs starts.

And can yo please explain this section to me:
“In the Source Backup Repositories window, select backup repositories from which OS data blocks must be retrieved.

It is strongly recommended that you select backup repositories on the same site where the target WAN accelerator is located. In the opposite case, the traffic will travel between sites, which will increase load on the network.”

This means that you should populate the Cache for the target WAN Accelerator from a repository located at the target site for your jobs, otherwise it will populate from the Source site which sends more traffic across your WAN.

So how would I populate it from the Target side repo if its empty,
That’s what I’m asking for. Do I need to manually copy the Backup files from Source to Target Repo then populate Target WAN Acceelerators from Target Repo?

Keep in mind @NemanjaJanicic - if you use High Bandwidth, which you say are going to do, and on both sides, Global Cache is not used, so pre-populating cache is moot:

Keep in mind @NemanjaJanicic - if you use High Bandwidth, which you say are going to do, and on both sides, Global Cache is not used, so pre-populating cache is moot:

 

So there is no need for me to pre populate cache, transfer full backup to off site location as initial seed?

I’m trying to wrap my head arround.
Yes we are going to use high bandwidth mode since our speed is arrounr 850 Mbps

Correct. No need to pre-populate cache as it’s not used with High Bandwidth mode. Read the link I provided in your previous post, bottom section, on how High Bandwidth is used. As I mentioned there also, Veeam doesn’t explicitly state how High Bandwidth is explicitly used, but I believe it just leverages “advanced” dedup and compression capabilities.

Hi @NemanjaJanicic - just following up with this post to see if there were any further questions you had? Let us know.