Storage Architecture

NFS Quota Agent runs as a lightweight, single-binary Go daemon on the NFS host server with root privileges.

Architecture Diagram

Kubernetes CSI Driver / Client
             │
             ▼ gRPC (:50051) / HTTP (:8080)
┌──────────────────────────────────────────────────────────┐
│  nfs-quota-agent Daemon (Go)                             │
│  ├─ gRPC Server (CreateQuota, SetQuota, DeleteQuota)    │
│  ├─ HTTP REST & Prometheus Metrics Exporter              │
│  ├─ Project ID Allocator (/etc/projects, /etc/projid)    │
│  └─ XFS Quota Controller (xfs_quota CLI / ioctl)         │
└──────────────────────────┬───────────────────────────────┘
                           │
                           ▼ Linux Kernel VFS / XFS Engine
┌──────────────────────────────────────────────────────────┐
│  /srv/nfs Filesystem (Mounted with 'pquota')             │
│  ├─ /srv/nfs/pvc-aaaa (Project ID 1001, Limit: 10 GiB)   │
│  ├─ /srv/nfs/pvc-bbbb (Project ID 1002, Limit: 50 GiB)   │
│  └─ /srv/nfs/pvc-cccc (Project ID 1003, Limit: 5 GiB)    │
└──────────────────────────────────────────────────────────┘

XFS Project Quota Kernel Mechanics

Mount Option: The XFS filesystem must be mounted with the pquota (or prjquota) option.
Directory Association: When a new PVC is created, a unique Project ID is assigned and linked to the directory:
```
xfs_quota -x -c 'project -s -p /srv/nfs/pvc-12345 101' /srv/nfs
```
Limit Enforcement: Hard and soft byte thresholds are established:
```
xfs_quota -x -c 'limit -p bhard=10g 101' /srv/nfs
```
Kernel-Level Blocking: Any write attempting to exceed the 10GiB limit immediately fails with EDQUOT (Disk quota exceeded).