My PC has a SSD for the root filesystem and the home directory and a large HDD for other data. From time to time I sync the SSD content to the HDD in case the SSD fails. The HDD has a separate backup.
Now I consider if I can use the BTRFS RAID modes to achieve the same. So can I use subvolumes with RAID mode, such that the SSD is mostly used for reads/writes and the data is synced to the HDD?
In addition, I would like to have snapshots of the volume on the HDD.
It would be great, when this would work without manual work, even when the HDD was disconnected for some time.
Another option would probably be btrfs send/receive, but a RAID mode which writes the HDD when the IO is idle would allow for always having a recent copy of the data.