I have a 12GB external drive that I setup with two partitions. One formatted as NTFS with 9300GB of space (Drive "X"), and the second as ReFS with 2450GB of space (Drive "V"). I had some corruption in the past while using ReFS, so that's why I have the majority of the space allocated as NTFS.

I have the below backup jobs configured:
Server - Entire Volumn (1.5TB) backed up with 10 day retention policy. GFS is configured to keep a full backup for 2 weeks and 1 full per month. I also have synthetic full backups set to create every Tuesday. Maintenance set to remove deleted after 7 days. This backs up to drive X with 9300GB of space

Workstations - Entire computer backed up with a 7 day retention. GFS is configured to keep a full backup for 3 weekly, 6 monthly, and 1 yearly. Synthetic full backups set to every Monday. Maintenance to remove deleted after 7 days. This backs up to drive V with 2450GB of space.

I also have the Workstation backup configured for a Backup Copy job which copies to drive X. Maybe this is not the best choice, but with the prior corruption on the ReFS formatted drive, I thought it would be good to have a copy going to an NTFS as well.
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I'm hopeful that someone could provide some guidance on perhaps some better settings. My server backup takes the most space so I've changed the retention policy to only keep backups for 7 days instead of 10. But the backups on the X drive are not falling off. The full backups also appear to be failing. Here is an image of the folder for the server backups.

Daily backups for my server is failing with the error "Failed to process method {Transform.CompileFIB}: There is not enough space on the disk."
How do I remove just the past several days worth of backups to free space up? It appears that changing the retention plan didn't clean them up.