Data Throughput Speeds b/w Amazon FSx for Windows file system and On-Premises using CloudWAN

Yes, what you're experiencing is not uncommon. Transfers from on-premises to Amazon FSx for Windows are often faster than the reverse. This difference mostly comes down to how the SMB (Server Message Block) protocol works.

SMB is the protocol used by FSx for Windows, and it wasn't really designed with long-distance or high-latency networks in mind (like across a WAN). It's very "chatty," meaning it needs a lot of back-and-forth communication between the client and server. That back-and-forth introduces delays, especially when you're pulling data from FSx to your on-premises environment.

On the other hand, writing data to FSx can be faster partly because FSx caches data in memory before writing it to disk, which speeds things up a bit.

To improve download speeds, I suggest:

1. Using tools like Robocopy with multi-threading enabled (/MT option).
2. Make sure your FSx file system has enough throughput capacity.
3. Look into WAN optimization tools.
4. Or, in some cases, use different protocols like SFTP if that's an option.

Hope this helps