Dataset snapshot and zpool size question

Hi everybody,

I’m fairly new to TrueNAS but managed to set up everything so far in a little home server.

I have a question regarding the pool size being reported and the replication process.

I am aiming to do a backup using replication task to a local usb attached drive which will then go offsite.

I already added the single drive and allowed it to be added as a new pool called backup and also created a dataset on it for the backup destination.

I just moved about 500gb from the source dataset to another on the same pool to allow headroom for the replication off to a 5TB drive. My source dataset was just above the capacity of the usb drive once it has been added into the vdev.

Now I see the 500gb in the new dataset but my source dataset has not dropped in size.

I am a newbie so go easy but I think it is because of snapshots referencing the source dataset?

If so I would like to use these to rollback the move after I copy off the backup to the da0 usb drive.

So my question is can I just run the replication and it will create a new snapshot automatically which will only copy the source dataset without the 500gb of data I moved, or will I have to delete the snapshots before I run the replication task to force it to do a new snapshot?

Thanks for any help on this folks.