swapDevices nixos module vs disko swap module: what's the difference, and which to use?

[TLATER]

@woodenAllen

Edit: I think that that module is for a separate swap partition, not a btrfs swapfile on a swap btrfs subvol…?

Yes, exactly. Disko is about partitioning your disk (hence the name). It won’t create files for you.

If you want to use swap files, use the NixOS option. I would advise against using swapfiles, though, especially if you’re using btrfs:

@TLATER

Really, the more I think about this the more I disrecommend using swap files. They’re anything but noob-friendly, inherently cause reproducibility issues, technically less performant due to the possibility of fragmentation, and an inherent data destruction risk with certain file systems. The only benefit is that they’re easy to resize, but that inherently causes the very fragmentation that makes them imperformant, so you should never actually do that (and nobody tells you this…). Plus, this is not the early 2000s, resizing filesystems is quite possible. If this is something you find yourself worried about just use LVM volumes.

See this summary in the thread in question on how to set up a swap file, too, but again, don’t actually do this. I’m pretty sure it will mess up your filesystem by default on btrfs.

@woodenAllen

And for the randomEncryption option, where do I set the config.randomEncryption?

For swap partitions configured with disko, like this.

If you want to change the encryption options, looks like for the time being you’ll have to manually set them in your NixOS configuration instead of through disko. Thanks to the NixOS module system multiple definitions of the same device will be merged constructively, so you can just redefine it and only set the encryption options.