Hyperbackup Eating all system resources since DSM 7?

I have a ds416j with 2 10 TB volumes with about 13TB used between the 2. I’m trying to run an initial hyper backup to an attached 16tb USB drive.

For some reason, the storage is now basically unusable while the backup is running. Accessing shares from a PC is brutally slow, and Plex (hosted on a different machine, but using NAS for storage) is effectively down. And of course, backing up 13 TB over usb 2 is going to take another week.

I’m pretty sure this didn’t happen with DSM 6? I originally created this backup without issues on that version, and recently wiped the drive and started over when the deltas filled up the space.

Has anyone else seen this problem? I know it’s probably time to upgrade to a newer model, but I’m not going to be comfortable doing that without a good backup, which means that isn’t really an answer to the current problem.

Thanks