mirror of
https://github.com/ryan4yin/nix-config.git
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110 lines
3.7 KiB
Nix
110 lines
3.7 KiB
Nix
{
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config,
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lib,
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...
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}:
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let
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cfg = config.modules.btrbk;
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in
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{
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# ==================================================================
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#
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# btrbk - scheduled LOCAL btrfs snapshots.
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# https://github.com/digint/btrbk
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#
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# Snapshots are created in `snapshotDir` (relative to the btrfs top-level
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# subvolume mounted at `volume`) and pruned by `snapshot_preserve`. With the
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# defaults they land in the @snapshots subvolume (mounted at /snapshots):
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#
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# /btr_pool/@snapshots/@persistent.<timestamp>
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#
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# These are same-filesystem snapshots: they protect against accidental
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# deletion and bad edits, NOT against disk loss. Off-host copies are handled
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# by restic (modules/nixos/base/restic-backup.nix), which can exclude the regenerable bulk
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# at the file level; btrbk works at the subvolume level, so a `target` would
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# also ship podman's overlay storage and the VM disk images. Set `target`
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# (plus `services.btrbk.sshAccess` on the receiving host) only if you want
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# that.
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#
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# The host MUST mount the btrfs top-level subvolume (subvolid=5) at `volume`;
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# this is enforced by an assertion so a missing mount fails evaluation instead
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# of failing silently at 3am.
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#
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# Restore a snapshot (offline; stop writers first):
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# 1. btrfs subvolume delete /btr_pool/@persistent
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# 2. btrfs subvolume snapshot /btr_pool/@snapshots/@persistent.<timestamp> \
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# /btr_pool/@persistent
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# 3. reboot, or remount /persistent, to pick up the restored subvolume.
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#
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# ==================================================================
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options.modules.btrbk = {
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enable = lib.mkEnableOption "scheduled btrfs snapshots via btrbk";
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volume = lib.mkOption {
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type = lib.types.str;
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default = "/btr_pool";
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description = "Mount point of the btrfs top-level subvolume (subvolid=5).";
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};
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subvolume = lib.mkOption {
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type = lib.types.str;
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default = "@persistent";
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description = "Source subvolume to snapshot, relative to {option}`modules.btrbk.volume`.";
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};
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snapshotDir = lib.mkOption {
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type = lib.types.str;
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default = "@snapshots";
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description = "Directory the snapshots are created in, relative to {option}`modules.btrbk.volume`.";
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};
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target = lib.mkOption {
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type = lib.types.nullOr lib.types.str;
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default = null;
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description = ''
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Optional off-host btrbk backup target (`target` in btrbk.conf). When
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null, only local snapshots are kept, which does not protect against
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disk loss.
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'';
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};
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onCalendar = lib.mkOption {
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type = lib.types.str;
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default = "Tue,Sat *-*-* 3:45:20";
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description = "systemd calendar expression for the snapshot timer.";
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};
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};
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config = lib.mkIf cfg.enable {
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assertions = [
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{
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assertion = builtins.hasAttr cfg.volume config.fileSystems;
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message = "modules.btrbk: no filesystem is mounted at `${cfg.volume}`; mount the btrfs top-level subvolume (subvolid=5) there so btrbk can snapshot `${cfg.volume}/${cfg.subvolume}`.";
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}
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];
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services.btrbk.instances.btrbk = {
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onCalendar = cfg.onCalendar;
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settings = {
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# keep daily snapshots for 7 days, and always keep 2 days worth.
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snapshot_preserve = "7d";
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snapshot_preserve_min = "2d";
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# retention for an optional off-host target.
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target_preserve = "9d 4w 2m";
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target_preserve_min = "no";
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volume.${cfg.volume} = {
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snapshot_dir = cfg.snapshotDir;
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subvolume.${cfg.subvolume} = {
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snapshot_create = "always";
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};
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}
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// lib.optionalAttrs (cfg.target != null) {
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target = cfg.target;
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};
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};
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};
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};
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}
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