I originally had typed out a lengthy breakdown of what I was experiencing and decided against it.

Question:

• What would cause performance to drop so much when in prior small and "large" tests it was great?
• Is it all processed in RAM before being written?

Basically the following:

• macOS
• Testing ZFS (successfully had writes in the 375 to 515 for RAID0) writing 20-280GB
• 32GB RAM after OS, Plex and services.
• Transferring ~9TB speeds were great until they slowed to what you see in the image.
  • A few occasional spikes to 280 but no higher than 350.
• Source is 3 x 6TB in raid0 , all barracudas. And yes going RAID0 to RAID0 is risky (
  • I have backups, planning to migrate full ZFS so I need to start shuffling around DATA
• Drives in another RAID 0 format (HFS ) was able to read at ~550MB/s and write ~490MB/s
• Drives in a 4x4TB = ~16TB raid0 in both setups.

I have gone from 7 hours fro completed copy to 9 to 11 to 16 hours and thats after 7 hours had passed.

https://preview.redd.it/unaqszjh9og11.png?width=342&format=png&auto=webp&s=f90bfaae777f60ef6539ea7fe91d8683dcd5814e