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Best way to keep a hot spare SD card for a raspberry pi? (sh.itjust.works)

submitted 3 months 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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[–] sugar_in_your_tea@sh.itjust.works 3 points 3 months ago (1 children)

Do you need a backup image?

For my NAS, all I do is:

keep notes of what's installed and how to configure OS things
automatic, offsite backups of important configs and data

Any full-disk backups just make the restore process easier, they're hardly the primary plan. If you want that, just take a manual backup like once a year, and maybe swap them out every 2-3 years (or however long you think the SD card should last). If you keep writes down, it should last quite a while (and nothing in your use-case seems write-heavy).

But honestly, you should always have a manual backup strategy in case something terrible happens (e.g. your house burns down). Make that your primary strategy, and hot spares would just be a time-saver for the more common case where HW fails.

[–] traches@sh.itjust.works 3 points 3 months ago (1 children)

Well, this is my DNS server which means if it’s down the internet is down and I can’t resolve hostnames to ssh into. I know that can be worked around, but I’d really like a quick and easy fix that I could even talk someone through over the phone if I had to.

My real backups are squared away, no worries. Nightly automatic restic snapshots, one to an external drive on this very pi and another to a NAS at my parents’ house.

[–] sugar_in_your_tea@sh.itjust.works 2 points 3 months ago* (last edited 3 months ago) (1 children)

I ended up making my router my DNS server, so if my router goes down, the internet is down anyway. I have static routes for things on my LAN, so if I hit mydomain.com, I can route it to an internal address instead of going over the internet. So far it works pretty well.

That said, I don't have a PiHole setup, so I don't know if that complicates things (I'm guessing pointing the router at the PiHole with a fallback to external DNS would just show ads or whatever if the PiHole is down).

But yeah, having a quick fallback is important. I think that should be as automatic as possible.

[–] traches@sh.itjust.works 1 points 3 months ago* (last edited 3 months ago) (1 children)

I like the DNS on the router idea, I’ll look into it. I do have some split DNS set up as well as adblocking lists (technitium). Not sure what my router can do.

Edit: autocorrect got me

[–] sugar_in_your_tea@sh.itjust.works 2 points 3 months ago

I think most can do it (esp. if you flash something like OpenWRT), but I have an entry-level enterprise router from Mikrotik and that's a pretty standard feature on that tier.