I've been on BackBlaze's Personal backup plan for a long long time and I'm hopeful I can stay on it as I migrate from an unvirtualized Windows 10 PC into a Windows 10 VM running on Unraid.
Currently all the data I'm interested in protecting is on a USB attached drive array. I'll migrate my BackBlaze license into a Windows 10 VM and just resume backing up that same USB attached disk array on day 1.
I've created a new, large ZFS pool and from day 2 forward, I will migrate big chunks of data into the ZFS pool and then serialize (zfs send) backups of the datasets back onto the attached USB. Once it's all backed up and tested, i can delete the original source directory on the USB attached disk array. By doing this one directory at a time (there are about 6-8 or so major directories), i wont need to 2x the data stored on the attached USB device.
It's going to take a long time but when I'm done, the attached USB device will just be backups and snapshots.
If anyone sees big holes in this, please let me know as I haven't started yet.