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Best way to keep a hot spare SD card for a raspberry pi? (sh.itjust.works)
submitted 2 years ago by traches@sh.itjust.works to c/selfhosted@lemmy.world
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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.

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[–] mumblerfish@lemmy.world 0 points 2 years ago (1 children)

Do you dd the device directly, and while it is running for this?

[–] Darkassassin07@lemmy.ca 0 points 2 years ago* (last edited 2 years ago) (1 children)

Yeah "dd if=/dev/mmcblk0 of=$HOSTNAME.$(date +%Y.%m.%d).img" and while its running. (!!! Make sure the output is NOT going to the sd card you are backing up....)

I deliberately chose a time when it's not very active to perform the backup. Never had an issue, going on 6 years now.

[–] Coelacanthus@lemmy.kde.social 2 points 1 year ago

Suggest use fsfreeze --freeze to block all access operation to create a stable image without unmount the SD card. (And release it later using fsfreeze --unfreeze.)

BTW, this feature was created by XFS and was moved to VFS in Linux 2.6.29 so all filesystems supported by Linux gained this feature.