feat(server): Add scrub stats

[patrickhampson]

Add scrub stats for pools by parsing zpool status

root@vault:~# curl -s http://localhost:9134/metrics | grep zfs_pool_scrub
# HELP zfs_pool_scrub_errors Number of errors detected during the most recent scrub or resilver.
# TYPE zfs_pool_scrub_errors gauge
zfs_pool_scrub_errors{pool="vault"} 0
# HELP zfs_pool_scrub_issued_bytes Bytes verified so far by the in-progress scrub or resilver, 0 if no scan is running.
# TYPE zfs_pool_scrub_issued_bytes gauge
zfs_pool_scrub_issued_bytes{pool="vault"} 8.565195580375e+12
# HELP zfs_pool_scrub_last_completed_timestamp_seconds Unix timestamp of the most recently completed scrub or resilver, or 0 if none.
# TYPE zfs_pool_scrub_last_completed_timestamp_seconds gauge
zfs_pool_scrub_last_completed_timestamp_seconds{pool="vault"} 0
# HELP zfs_pool_scrub_rate_bytes_per_second Current scan rate of the in-progress scrub or resilver, 0 if no scan is running.
# TYPE zfs_pool_scrub_rate_bytes_per_second gauge
zfs_pool_scrub_rate_bytes_per_second{pool="vault"} 8.81852416e+08
# HELP zfs_pool_scrub_repaired_bytes Bytes repaired during the most recent scrub or resilver.
# TYPE zfs_pool_scrub_repaired_bytes gauge
zfs_pool_scrub_repaired_bytes{pool="vault"} 0
# HELP zfs_pool_scrub_scanned_bytes Bytes read so far by the in-progress scrub or resilver, 0 if no scan is running.
# TYPE zfs_pool_scrub_scanned_bytes gauge
zfs_pool_scrub_scanned_bytes{pool="vault"} 1.143492092887e+13
# HELP zfs_pool_scrub_state State code for the most recent scrub or resilver [0: none, 1: scrub_in_progress, 2: scrub_finished, 3: scrub_canceled, 4: scrub_paused, 5: resilver_in_progress, 6: resilver_finished].
# TYPE zfs_pool_scrub_state gauge
zfs_pool_scrub_state{pool="vault"} 1
# HELP zfs_pool_scrub_total_bytes Total bytes to scan in the in-progress scrub or resilver, 0 if no scan is running.
# TYPE zfs_pool_scrub_total_bytes gauge
zfs_pool_scrub_total_bytes{pool="vault"} 3.3205251158835e+13

[patrickhampson]

@pdf bump on reviewing this one.

[pdf]

Hi @patrickhampson sorry for the delay on this - I've just moved to the other side of the world and don't have access to my lab atm, should be back up and running in a month or two.