I have a load-bearing raspberry pi on my network - it runs a DNS server, zigbee2mqtt, unifi controller, and a restic rest server. This raspberry pi, as is tradition, boots from a microSD card. As we all know, microSD cards suck a little bit and die pretty often; I’ve personally had this happen not all that long ago.

I’d like to keep a reasonably up-to-date hot spare ready, so when it does give up the ghost I can just swap them out and move on with my life. I can think of a few ways to accomplish this, but I’m not really sure what’s the best:

  • The simplest is probably cron + dd, but I’m worried about filesystem corruption from imaging a running system and could this also wear out the spare card?
  • recreate partition structure, create an fstab with new UUIDs, rsync everything else. Backups are incremental and we won’t get filesystem corruption, but we still aren’t taking a point-in-time backup which means data files could be inconsistent with each other. (honestly unlikely with the services I’m running.)
  • Migrate to BTRFS or ZFS, send/receive snapshots. This would be annoying to set up because I’d need to switch the rpi’s filesystem, but once done I think this might be the best option? We get incremental updates, point-in-time backups, and even rollback on the original card if I want it.

I’m thinking out loud a little bit here, but do y’all have any thoughts? I think I’m leaning towards ZFS or BTRFS.

  • ShadowEnglish
    4•3 months ago

    Why not just connect an ssd via USB and save yourself the hassle and torment?

    • Avid AmoebaEnglish
      1•3 months ago

      That wouldn’t solve the problem though would it? It might make it less likely to fail but there’s still significant downtime if there’s no hot spare for this USB drive.

      • ShadowEnglish
        3•3 months ago

        I couldn’t count the number of failed sd cards I’ve seen across all my fingers and toes.

        I’ve seen like 4 ssds in my entire life fail. Plus you could just do mdraid 1 / btrfs across 2 of them if you want

        • Avid AmoebaEnglish
          0•3 months ago

          Any failures of SanDisk Extreme Pro / Samsung Evo Plus?

          I buy the redundancy argument. I’d still use ZFS for that if possible though. 😂 All my machines use mdraid 1 for their system drives but now that I know enough about ZFS, I’d likely use it on root next time around.

          • ShadowEnglish
            3•3 months ago

            Yes. I’ve always splurged on nice cards for my personal stuff. I think it’s more about the write behavior of Linux than anything else, since I’ve never had a card die in my camera.

            I refuse to use a pi with SD at this point. Saving $50 isn’t worth my time to reinstall things.

            • Avid AmoebaEnglish
              1•3 months ago

              You’re making me nervous.

              But then again, all my Pis are OpenWrt now which barely writes, so I’m probably fine. 😅