Sync root filesystem

[rlogiacco]

(4th Aug, 2014 08:08 PM)CurlyMo Wrote:  Why not create a BTRFS mirror with the SD card and your USB stick?

Can you expand on this? If btrfs mirror implies copying over the snapshots I don't think it is desiderable: a lot more write operations toward the SD, much more space used and a very little benefit considering the SD is going to be used only "on the go". If something breaks and I need to revert to a previous snapshot I'll do it on the HD and force a re-sync to ensure I have a stable OS on the HD and on the SD.
If that doesn't imply moving the snapshots then I will definitely be interested.

UPDATE: I've read a bit about mirroring and it looks as a soft raid... While I do understand it's cleanness and advantages it doesn't seem to fit my needs: too many read/writes to the SD card for my tastes

(4th Aug, 2014 08:08 PM)CurlyMo Wrote:  In regard to your last question. You are not using BTRFS in any way in that approach.

I agree, I'm not using any benefit from btrfs that I know, but I don't know btrfs so I don't know what can I do with it. With my lack of knowledge I went for the route I already know with a slight change to what I understood about btrfs layout, but I might be totally wrong.... And I wish to avoid corrupting my OS :-D

For what I have understood I cannot create a snapshot on one drive and copy it over the other as that wouldn't work: snapshots are incremental and based on filesystem state. A raid configuration is not optimal as it will use the two storages at the same time, while I want to preserve the SD... what options do I have?

UPDATE: I believe I could avoid the cumbersome mount /mnt/sd-rootfs/@/root and at least use btrfs feature to automatically mount the root partition in it's default state, then issue the rsync command and unmount it: this should at least remove the complexity of manually handling the correct data tree.
For security and stability reasons I can even create a snapshot before each rsync operation to be able to revert my changes: I understand snapshots are really cheap.
Do you believe this would work?