collector/mdadm: Support RAID metrics

[rexagod]

Use sysfs for RAID stats. Also added tests for the collector.

Fixes: #842

[rexagod]

Not sure what's causing the error here, the logs seem okay (no level=error lines)?

[discordianfish]

The log indicates a diff between metrics and expected metrics:

--- collector/fixtures/e2e-output.txt 2024-06-21 23:39:55.007539384 +0000
+++ /tmp/node_exporter_e2e_test.UZ2v15/e2e-output.txt 2024-06-21 23:42:36.000289912 +0000
@@ -1581,6 +1581,14 @@
node_md_blocks_synced{device="md7"} 7.813735424e+09
node_md_blocks_synced{device="md8"} 1.6775552e+07
node_md_blocks_synced{device="md9"} 0
+# HELP node_md_degraded Number of degraded disks on device.
+# TYPE node_md_degraded gauge
+node_md_degraded{device="md0"} 0
+node_md_degraded{device="md1"} 0
+node_md_degraded{device="md10"} 0
+node_md_degraded{device="md4"} 0
+node_md_degraded{device="md5"} 1
+node_md_degraded{device="md6"} 1

HELP node_md_disks Number of active/failed/spare disks of device.

TYPE node_md_disks gauge

node_md_disks{device="md0",state="active"} 2
@@ -1653,6 +1661,14 @@
node_md_disks_required{device="md7"} 4
node_md_disks_required{device="md8"} 2
node_md_disks_required{device="md9"} 4
+# HELP node_md_raid_disks Number of raid disks on device.
+# TYPE node_md_raid_disks gauge
+node_md_raid_disks{device="md0"} 2
+node_md_raid_disks{device="md1"} 2
+node_md_raid_disks{device="md10"} 4
+node_md_raid_disks{device="md4"} 3
+node_md_raid_disks{device="md5"} 3
+node_md_raid_disks{device="md6"} 4

HELP node_md_state Indicates the state of md-device.

TYPE node_md_state gauge

node_md_state{device="md0",state="active"} 1

[rexagod]

Ah! It seems I didn't update the e2e output manifest, so the unit test was working fine for me, but the e2e ones were failing. Updated.

[discordianfish]

LGTM!

[rexagod]

cc @SuperQ 🙂

[SuperQ]

This needs a rebase to pick up the replacement slog logging.