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Best way to keep a hot spare SD card for a raspberry pi? (self.selfhosted)

submitted 3 months ago by traches to c/[email protected]

54 comments fedilink hide all child comments

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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[–] [email protected] 1 points 3 months ago* (last edited 3 months ago) (1 children)

The issue is that I don't think its standard bootloader supports booting from RAID. I guess you could use a MicroSD for booting then have everything else on the RAID1. There's unofficial ways to boot using GRUB, which should work with RAID1 too.

[–] [email protected] 2 points 3 months ago (1 children)

Grub supports software raid just fine. The main issue is that you need to modify grub configuration to add bootloader on both drives, but even if you don't it's pretty simple to recreate needed files for second drive when the primary one dies.

[–] [email protected] 2 points 3 months ago

GRUB does, but Raspberry Pis don't use GRUB by default. You should be able to install it, but it's not officially supported.