The ZFS tab shows the ARC, and names every caching tier a pool has or lacks

A Cache section between the pools and the schedules. One card for the ARC:
size against its ceiling with the target and floor, sparklines of size and
hit rate from the sampler's history, what it holds (MRU/MFU/dirty, data vs
metadata, compression, the ghost lists), the prefetcher and dbuf cache, the
memory-pressure counters, and the since-boot breakdown by demand/prefetch
and data/metadata. Then a card per pool for L2ARC, SLOG, special vdev,
dedup table and spares — the devices and their fill where they exist, and
where they don't, plainly none and what that means (the ZIL writing to the
pool's own vdevs, with how much it has written).

Live numbers come from the sampler, which reads arcstats every tick and
publishes zfs.arc.* sensors; the fuller picture is read on request, with
zpool list -Hpv and zfs get run without sudo and cached for thirty seconds.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

SENSORS.md

@@ -21,6 +21,7 @@ disk.<dev>.read|write|util|size|temp
 fs.<mount>.size|used|used_pct
 ups.battery|runtime|load|load_pct|in_v|out_v|on_battery|state|source
 gpu.<name>.usage|render|video|video-enhance|copy|compute|temp|power|fan|freq|mem_used|mem_total|clients
+zfs.arc.size|target|min|max|mru|mfu|data|metadata|hit_pct|reads|misses|lifetime_hit_pct|no_grow|compress_ratio|l2_size|l2_hit_pct
 ```
 
 - Segments are lower case `[a-z0-9_-]`: `Package id 0` → `package_id_0`, `/mnt/tank` →
@@ -42,6 +43,10 @@ gpu.<name>.usage|render|video|video-enhance|copy|compute|temp|power|fan|freq|mem
   has it open. `temp` is the card's own sensor, or on an integrated GPU the CPU package it
   shares a die with (label `source` says which); an Arc on i915 has none and reports none.
   `freq` is the actual clock, 0 when power-gated. `clients` counts the processes using it.
+- `zfs.arc.*` is the ZFS read cache in RAM, on a machine with the module loaded. `hit_pct`
+  is over the last sampling interval and appears once an interval has had any reads (an idle
+  interval repeats the last value); `lifetime_hit_pct` is since boot. `no_grow` is true
+  while memory pressure stops the cache growing. `l2_*` appear only with cache devices.
 
 ## A sensor