# longhorn-capacity — A Longhorn volume or node is near its storage capacity

**Alerts:** `LonghornVolumeCapacityHigh` (warning, 30m) and `LonghornNodeStorageHigh` (warning, 30m)
**File:** `platform/monitoring/alerts.yaml`, group `platform-health.longhorn`
**Expressions:**
`(longhorn_volume_actual_size_bytes / longhorn_volume_capacity_bytes) > 0.85`
`(longhorn_node_storage_usage_bytes / longhorn_node_storage_capacity_bytes) > 0.85`

## What this means here

Either one volume is 85% full, or one node's Longhorn disk is 85% allocated. They are different
problems with different fixes, so read the labels: `volume` means a workload is filling its own PVC;
`node` means the cluster is running out of places to put replicas.

The node case is bounded by settings that are already conservative:
`storageReservedPercentageForDefaultDisk: 20`, `storageMinimalAvailablePercentage: 25`,
`storageOverProvisioningPercentage: 200`, `defaultDataLocality: disabled`, hard node anti-affinity.
Measured headroom on prod is roughly **269 GiB scheduled against an 829 GiB ceiling**, so the node
alert firing means something has changed materially, not that the platform has slowly grown.

The severe consequence of running out of node storage is that a degraded volume **cannot finish
rebuilding** — hard anti-affinity needs three distinct nodes with room, so one full node pins a
volume at 2 replicas indefinitely. Cross-read `/runbooks/longhorn-degraded`.
### Verify the alert can even fire (measured 2026-09-13)

Prometheus on prod scrapes 19 jobs: `apiserver`, `cdi-prometheus-metrics`, `coredns`,
`keycloak-discovery`, `keycloak-service`, `keycloak/keycloak-db`, `kube-prometheus-stack-alertmanager`,
`kube-prometheus-stack-grafana`, `kube-prometheus-stack-operator`, `kube-prometheus-stack-prometheus`,
`kube-state-metrics`, `kubelet`, `kubevirt-prometheus-metrics`, `nextcloud-db/nextcloud-db`,
`node-exporter`, `oauth2-proxy`, `semaphore-db/semaphore-db`, `velero`, `velero/node-agent`.
There is **no** Longhorn, cert-manager, Flux-controller or Hubble/Cilium job. Check the series this
rule depends on before you trust its silence:

```
infra/devcontainer/dev.sh run bash -c \
  'kubectl --context k3s-prod -n monitoring port-forward svc/kube-prometheus-stack-prometheus 19090:9090 & \
   sleep 5; curl -s -G --data-urlencode "query=count by (job) (up)" localhost:19090/api/v1/query'
```

**These alerts are currently INERT.** `count(longhorn_volume_capacity_bytes)` and
`count(longhorn_node_storage_capacity_bytes)` both returned **0 series** on prod on 2026-09-13 —
Longhorn ships no ServiceMonitor here. Volume-fill coverage actually comes from
`kubelet_volume_stats_*` instead, i.e. `/runbooks/pvc-capacity`, which is where the working alerts
are. Use this runbook for the Longhorn-side (node allocation) half, and expect to reach it by hand.
## Running the commands in this runbook

`kubectl` does not work on the operator workstation. The toolchain lives only in the pinned dev
container, and the host's `k3s-oidc` context hangs on a browser prompt once its token expires —
that hang is not the cluster being down. Every command below runs as:

    infra/devcontainer/dev.sh run bash -c 'kubectl --context k3s-prod get nodes'

Always pass `--context k3s-prod` explicitly. `dev.sh` merges BOTH clusters into one kubeconfig and
picks a current-context per invocation, and **that default has already changed once** — it was k3s-dev
until dev was decommissioned on 2026-09-13, and is k3s-prod now. A command that names its context means
the same thing next month as it does today; one that relies on the default does not, and the failure is
silent (it answers confidently about the other cluster). `CLUSTER=prod infra/devcontainer/dev.sh run
kubectl ...` selects it explicitly, and every invocation prints a banner naming the cluster it is about
to talk to — read it. Do not run two `dev.sh` invocations at once; they share one container and
interfere.

USE FULLY-QUALIFIED RESOURCE NAMES, ALWAYS. Three CRDs on this cluster register the kind `Backup`:
`longhorn.io/v1beta2`, `postgresql.cnpg.io/v1` and `velero.io/v1`. The bare short name resolves to
Longhorn's, which holds zero objects — so `kubectl get backup -A` prints **"No resources found"** on
a cluster holding 6 Velero backups and 27 CNPG backups. Verified on prod 2026-09-13. Reading that as
"the backups are gone" and acting on it turns a false negative into real data loss. Write
`backups.velero.io`, `backups.postgresql.cnpg.io`, `clusters.postgresql.cnpg.io`,
`settings.longhorn.io`, `volumes.longhorn.io`, `nodes.longhorn.io`.

Mutating kubectl (`apply`, `patch`, `annotate`, `rollout`) and `flux reconcile` are blocked for
agents here: every durable change goes through git (`git push origin main` **is** the deploy).
Where this runbook gives a mutating command it is for an operator, and it says so.

## First commands

Node-level allocation (the half that has no substitute alert):

```
infra/devcontainer/dev.sh run bash -c \
  'kubectl --context k3s-prod -n longhorn-system get nodes.longhorn.io -o yaml | grep -E "name:|storageAvailable|storageMaximum|storageScheduled|allowScheduling"'
```

Volume sizes versus actual usage:

```
infra/devcontainer/dev.sh run bash -c \
  'kubectl --context k3s-prod -n longhorn-system get volumes.longhorn.io \
     -o custom-columns=NAME:.metadata.name,SPEC:.spec.size,ACTUAL:.status.actualSize,ROBUST:.status.robustness'
```

Which PVC each one is, so you know who is filling it:

```
infra/devcontainer/dev.sh run bash -c \
  'kubectl --context k3s-prod get pv -o custom-columns=PV:.metadata.name,CLAIM:.spec.claimRef.namespace/.spec.claimRef.name,SIZE:.spec.capacity.storage,SC:.spec.storageClassName'
```

The filesystem view, which is the alert that actually works:

```
infra/devcontainer/dev.sh run bash -c \
  'kubectl --context k3s-prod -n monitoring port-forward svc/kube-prometheus-stack-prometheus 19090:9090 & sleep 5; \
   curl -s -G --data-urlencode "query=topk(10, 1 - kubelet_volume_stats_available_bytes{job=\"kubelet\"} / kubelet_volume_stats_capacity_bytes{job=\"kubelet\"})" localhost:19090/api/v1/query'
```

On the node itself:

```
ssh k3s-prod-1 'df -h /data; du -xh --max-depth=1 /data/longhorn/replicas 2>/dev/null | sort -h | tail'
```

## Likely causes, most likely first

### 1. A CNPG database is not recycling WAL (check this FIRST)
The only cause here that grows without bound. `archive_mode=on` plus a failing `archive_command` means
Postgres will not recycle unarchived WAL; measured on prod `keycloak-db` at ~6.8 MiB/h with `pg_wal`
sharing the data PVC (no `walStorage:` is configured on any Cluster) — about 29 days from 93% free to
disk-full, ending in a postmaster PANIC. Go to `/runbooks/cnpg-archiving`. **Never delete WAL by
hand.**

### 2. Snapshots and orphaned replicas accumulating
Longhorn snapshots are not free, and cleanup here is **manual**: `orphanAutoDeletion: true` in
`platform/longhorn/helmrelease.yaml` has been **silently inert since Longhorn 1.12** — it was renamed
`orphanResourceAutoDeletion` (now a list) and the chart drops unknown `defaultSettings` keys with no
error. Verify the key's current state in that file before citing it; then prune orphans and stale
snapshots from the Longhorn UI.

### 3. A workload genuinely grew
Plex/Sonarr/Radarr **media** does not live on Longhorn — it is static NFS from
`192.168.2.102:/mnt/Storage/plex`, via the `bulk` tier. If a media volume is on `longhorn`, that is a
misconfiguration worth fixing, not a capacity problem: the `bulk` StorageClass is a stub
(`provisioner: nfs.csi.k8s.io`, `server:/share: REPLACE-ME`) and provisions nothing, so real bulk
storage is static NFS PVs. Otherwise expand the PVC — all Longhorn classes have
`allowVolumeExpansion: true`; change the size in git and push.

### 4. Replicas piled onto one node
`replicaAutoBalance: best-effort` should prevent this, and hard anti-affinity bounds it to one replica
per volume per node. If one node is much fuller than the others, check whether a rebuild placed
replicas there while another node was down.

### 5. The cluster has outgrown its disks
Prod's ceiling is ~829 GiB across three nodes. `docs/plans/longhorn-ssd-tiering.md` is the planned
answer (a ~51 GB hot tier: Prometheus, CNPG, Loki, Gitea). Operator planning work.

## When to escalate or stop

- **A node over 85% while any volume is degraded is urgent**, because the rebuild cannot complete.
  Free space or restore the other node before anything else.
- **Never delete files under `/data/longhorn`** or inside a Postgres `pg_wal`. Both are irreversible.
- **Do not expand a PVC as a reflex** if the cause is unrecycled WAL — you are buying days and hiding
  the real fault.
- Escalate for adding disks, the SSD tiering plan, or anything that needs a node reboot (each reboot
  degrades all ~18 volumes and triggers a rebuild storm).

---
Source of truth: `runbooks/longhorn-capacity.md`. Index: `/runbooks/`
Records: `platform/longhorn/helmrelease.yaml` (the settings above and the inert `orphanAutoDeletion`);
`platform/cnpg/alerts.yaml` header (the WAL disk-full clock); `docs/BULK-NFS-STORAGE.md`.