zfs_config also says what the module says before it leaves a node (Z17): the next load of the kernel module uses ZFS's defaults, the three units and /etc/hostid stay.
Builds: design 42 zfs-owns-zfs §28, §30, §10, A-31, A-35
The safety review of the first version found it safe for the pool's data and asked for these fixes before
it goes on the home server:
- zfs_snapshot: no recursive. Every answer gives the dataset's free space and the pool's capacity, and
says that the snapshot holds every block deleted or overwritten until it is destroyed by hand.
- A command that runs out of time is ended with its whole process group. An act that timed out is
answered from the list, or as "outcome unknown", never as "NOT DONE".
- The watch runs as the operator account.
- The event follower reads ZFS's queue from its start, with a cursor per boot, so the pool's import and
any downtime reach the journal once. It writes "dropped N events", kills zpool before waiting for it,
and exits non-zero after five failed follows in a row.
- Past error counts are a warning, and counts that rise are unhealthy.
- The guard test catches .Run(, exec.Command(, exec.CommandContext( and process starts.
- The fixtures and the parser follow OpenZFS 2.4.4's own printers: human scan sizes under -p, no iostat
section lines, error scrubs, per-vdev rebuild resilvers, paused scrubs.
The operator also asked the module to own the scrub. A timer and a service of the module's own run
zpool scrub -w -- <pool> from the scrub-pool, scrub-cadence, scrub-day and scrub-time settings. In the
same declaration, the distribution's weekly and monthly timers for that pool are held stopped and
disabled, so exactly one schedule scrubs it. zfs_scrub shows the schedule and the next run, with any
resilver's progress. zfs_scrub_start, zfs_scrub_pause and zfs_scrub_stop act with why. The health check
warns of a late or failed scrub and of a running resilver, and is unhealthy for a resilver that finished
with errors.
The home server's pool holds the operator's media library, and no mesh tool could say whether it is
healthy, how full it is, when it was last scrubbed or what snapshots exist; the only way was a login.
This module reads all of it with fixed zfs and zpool commands (list, get, status, iostat, events,
history) and has one act, zfs_snapshot, which only adds a snapshot: refused for an unknown dataset, a
name outside [A-Za-z0-9._-], an existing snapshot or no why; run as sudo -n zfs snapshot -- ds@name;
answered from zfs list afterwards, with any other snapshot that came or went meanwhile; recorded as the
event snapshot.taken. No destroy, rollback, set or send exists, and a test holds every command to its
verb.
Health (ADR 0240): zfs_health on the watch process, unhealthy for a pool not ONLINE, device or data
errors, a pool past 90 % full or no ZFS at all; past 80 % and a scrub older than 35 days are warnings.
Beside it, the event follower (zpool events -f, as root) keeps ZFS's errors in its journal past a
reboot and is judged by its unit, the check the module does not run itself. No seat (ADR 0121), no
package: ZFS is the machine's.
jschoubben
jochen