Longhorn: Distributed Block Storage for Kubernetes Bare Metal

What Is Longhorn?

Longhorn provides distributed block storage for Kubernetes — no cloud provider required. Built for bare-metal clusters, edge deployments, and on-prem infrastructure. CNCF Incubating, 6K+ stars.

Why Longhorn for Bare Metal?

Installation

helm repo add longhorn https://charts.longhorn.io
helm install longhorn longhorn/longhorn \
  --namespace longhorn-system \
  --create-namespace \
  --set defaultSettings.defaultReplicaCount=3

How It Works

┌──────────────────────────────────────────────────┐
│                Longhorn Manager                    │
└──────────────────────┬───────────────────────────┘
                       │
    ┌──────────────────┼──────────────────┐
    │                  │                  │
┌───▼────┐       ┌────▼───┐        ┌────▼───┐
│ Node 1 │       │ Node 2 │        │ Node 3 │
│┌──────┐│       │┌──────┐│        │┌──────┐│
││Replica││       ││Replica││        ││Replica││
││  1    ││       ││  2    ││        ││  3    ││
│└──────┘│       │└──────┘│        │└──────┘│
│ /dev/sdb│       │ /dev/sdb│        │ /dev/sdb│
└────────┘       └────────┘        └────────┘

Each volume has 3 replicas across different nodes. If a node dies, data survives.

StorageClass

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: longhorn-fast
provisioner: driver.longhorn.io
parameters:
  numberOfReplicas: "3"
  staleReplicaTimeout: "2880"
  diskSelector: "ssd"  # Target SSD disks only
  nodeSelector: "storage"
reclaimPolicy: Delete
volumeBindingMode: Immediate
allowVolumeExpansion: true

Backup to S3/MinIO

# Backup target configuration
apiVersion: longhorn.io/v1beta2
kind: Setting
metadata:
  name: backup-target
  namespace: longhorn-system
value: "s3://longhorn-backups@us-east-1/"
---
apiVersion: longhorn.io/v1beta2
kind: Setting
metadata:
  name: backup-target-credential-secret
value: "longhorn-s3-secret"

Schedule automatic backups:

apiVersion: longhorn.io/v1beta2
kind: RecurringJob
metadata:
  name: daily-backup
  namespace: longhorn-system
spec:
  cron: "0 2 * * *"
  task: backup
  retain: 7
  concurrency: 2
  labels:
    tier: production

Disaster Recovery (Cross-Cluster)

┌──────────────┐         ┌──────────────┐
│   Primary    │  backup  │   DR Site    │
│   Cluster    │────────▶│   Cluster    │
│              │  (S3)    │              │
│  Longhorn    │         │  Longhorn    │
│  Volumes     │         │  (standby)   │
└──────────────┘         └──────────────┘

Volumes replicated to S3; DR cluster restores from same bucket. RPO depends on backup frequency (hourly = 1h RPO).

Performance Tuning

# High-performance settings
defaultSettings:
  guaranteedInstanceManagerCPU: 12  # Dedicated CPU for I/O
  storageOverProvisioningPercentage: 200
  storageMinimalAvailablePercentage: 15
  replicaAutoBalance: best-effort

# For database workloads
parameters:
  numberOfReplicas: "2"  # Trade durability for performance
  dataLocality: "best-effort"  # Prefer local replica

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