So I am moving 6.9 TB of data to my new Proxmox server, on the "from" server it states that it is 6.9 TB, in the CLI on the proxmox server it says the same.
The GUI though says 7.45 TB.
How come?
And don't forget the overhead. Especially when using a raidz1/2/3 you often get alot of padding overhead. Lets say you write 1TB to a zvol and that zvol will then need 1.66 TB on the pool. That additional 0.66 TB come from the padding overhead when you use raidz1/2/3 without increasing the volblocksize. Snapshot can also consume alot of additional space. And make sure the complete TRIM/discard chain from guest OS to physical Disks is working or your ZFS pool wouldn't be able to free up space after deleting stuff, which will result in a pool that will grow and grow over time.