Balancing multiple files to multiple drives with high end temp ssd

[pest]

I've tried to read up on balancing limitation but I am either still missing something or my setup is not configured/working correctly.  

NAS Configuration:

Folder duplication on the entire drive pool (including temp).

NAS Hardware:

2x 500GB NVME WD Black drives (temp SSD optimizer storage with rules to auto balance)

6x WD RED's varying (3x10TB, 1x6TB, 2x4TB)

 

I'm able to transfer from workstation to NAS > 1000MB/s over 10gbe to the NVME temp.

When the NAS has MULTIPLE files to balance, it only migrates (and maxes out) 1 HDD at a time (see attached).

My attachment is transferring ~10 files of ~40GB from my temp drives to the spinning rust archives.

At least 4 out of 5 HDD have open space to transfer to based on the 90% fill rule.

 

Currently it moves from 1 NVME to 1 HDD at a time, maxing out the HDD speed for each drive.

Shouldn't this hit AT LEAST 2 HDD (1 for each NVME) or better yet max with multiple HDD per NVME given available multiple file transfers.

In this example, my 2 NVME drives can saturate 5 HDD throughput of 10 files of 40GB at the same time.

 

What am I missing?  Does the single thread limitation still apply for multiple files from multiple drives to multiple sources (lol) ?

[Shane]

I believe the short answer is that single-file-at-a-time balancing was by far the simplest and safest to code*, so guaranteed reliability (and more time to code other things) was chosen over raw speed.

*In my very limited and outdated experience, multi-threaded operations are fantastic when you can just tick a checkbox in a compiler that can safely (hah) optimise it all for you, and a complex pile of risk conditions when you have to write it yourself.

[pest]

Yea I couldn't find if it was truly only single file or single file to a single drive, where in my case there are multiple files and multiple drives to be utilized.  Not sure how many others use multiple temp drives so maybe I'm a fringe case.