Persistent Volume

Here's the technical breakdown of using VirtualBox Shared Folders vs NFS for persistent storage in your k3s cluster:

1. Technical Possibility ✅

Yes, you can use VirtualBox Shared Folders as persistent storage through hostPath volumes, but with significant limitations compared to NFS.

2. Implementation Method

Step 1: Mount Shared Folder in VMs

# On both VM1 and VM2
sudo mount -t vboxsf <shared_folder_name> /mnt/shared

Step 2: Create PersistentVolume

apiVersion: v1
kind: PersistentVolume
metadata:
  name: vbox-shared-pv
spec:
  capacity:
    storage: 100Gi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  hostPath:
    path: /mnt/shared
    type: Directory

Step 3: Create PersistentVolumeClaim

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: vbox-shared-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi

3. Critical Limitations ⚠️

Aspect	VirtualBox Shared Folders	NFS
Concurrent Access	Single-writer only	Multi-writer supported
File Locking	No proper advisory locks	Full locking support
Permissions	UID/GID mapping issues	POSIX permissions
Performance	Slow for small files	Better throughput
Pod Scheduling	Tied to specific nodes	Any node
Atomic Renames	Not supported	Supported
Symlinks	Partial support	Full support

4. Specific Application Risks 🚨

Database Corruption (Vaultwarden/PostgreSQL):

# Common error you might see:
FATAL:  could not flush dirty data: Invalid argument

File Locking Issues (Paperless-ngx/Nextcloud):
```
Error: Failed to acquire advisory lock on file
```

Permission Mismatches:

www-data user cannot write to shared folder

5. Recommended Workflow 🔄

If you still want to proceed:

Use only for read-only volumes

Add to pod specs:

securityContext:
runAsUser: 1000
fsGroup: 1000

Regular backups:

# Add to crontab
0 * * * * rsync -a /mnt/shared/ /mnt/backup/$(date +\%s)

6. Better Alternative ✅

Use NFS through VirtualBox Shared Folders:

On Physical Machine 1:

# Share via NFS instead of vboxsf
/mnt/host-share 192.168.123.221(rw,sync) 192.168.123.222(rw,sync)

Mount in VMs:

mount -t nfs 192.168.123.100:/mnt/host-share /mnt/nfs-share

7. When to Consider Shared Folders

Single-node development clusters
Read-only configmaps/secrets
Temporary scratch space
Non-critical data with regular backups

For your production-like home lab with stateful applications, NFS remains the better choice for data integrity and multi-node access.