add btrfs storage to /home

If you're going to merge with the / volume here are some things that need to be thought about.

1. Does the boot process scan correctly for multi partition btrfs volumes?
2. If you remove the card your volume will be incomplete: if set up without redundancy I.E. raid0, jbod then the volume is incomplete and can't be used, card can not be removed while phone is active at all, inclusive of set alarms.
3. If the card fails, incomplete volume total data loss likely, then its 1 back to Jolla Care for a fresh flash of primary OS, unless you've got a disk image of original OS, then you'll need to restore it manually.
4. You can not share the card with any other device, as it might try and restore/format the partition. I.E. corrupt the card see point 3. Therefore make one partition and lock the card in the Jolla.
5. If the card is slow it could slow the whole FS.
6. Something I've likely forgotten.

Advantages of adding a card to the / volume I see are

1. Easy expansion of space that is shared effectively.
2. If it's a quick card, could improve Disk IO as it'll be split between 2 physical flash devices.
3. Lost phone, most likely if the person with your now lost/stolen phone is malicious they'll rip card out and try to read it's contents, being an incomplete volume, it'll be nearly useless for them, which means they'll have to break any code on the phone to easily retrieve any data, if they haven't already trashed the partition on the card.
4. Wear leveling the flash drive.
5. Again something I've likely forgotten.

Hey, for your question about 1) yes the jolla subvolume is being set default so the jolla-mountsd script mounts it just like any other card.

With your idea to add your sd to the rootfs or @home, there is a whole thread about that on http://talk.maemo.org and I strongly suggest to not do it. Why? Because Jolla may do funky things as they like and for sure they do not consider you having your uSD integrated into / or /home when upgrading. So if need be, mount uSD to /home/nemo completely but not integrated. That way you have internal storage @home still functional if the uSD mount breaks/fails, for / you better have a flashable image at hand when tinkering with it. Playing with the internal storage device can easily brick your phone for good. In future upgrades the uSD will be more utilized automatically for eg camera default storage among other things. So if you have trouble getting your internal storage consumption down I suggest you move irrelevant data off site only. I moved Android's user-data folder only as that is what consumes most of the space. It is also shared, in terms, both mounts make use of all of your uSD.