9P File Access
The 9P protocol provides an alternative way to mount ZeroFS on Linux systems. Originally from Plan 9, the 9P2000.L variant is optimized specifically for Linux and can offer better performance than NFS for certain workloads.
9P provides correct fsync semantics, making it the preferred choice for applications that require durability guarantees (databases, transactional systems). NFS has limitations with fsync due to its COMMIT protocol design.
Installation
9P support is included in the Linux kernel. You may need to load the module:
# Load 9P modules
sudo modprobe 9p
sudo modprobe 9pnet_tcp
# Verify modules are loaded
lsmod | grep 9p
Basic Usage
Mounting ZeroFS
# Create mount point
sudo mkdir -p /mnt/zerofs-9p
# Mount via 9P
sudo mount -t 9p -o trans=tcp,port=5564,version=9p2000.L 127.0.0.1 /mnt/zerofs-9p
Unmounting
sudo umount /mnt/zerofs-9p
Mount Options
Required Options
| Option | Description |
|---|---|
trans=tcp | Use TCP transport |
port=5564 | ZeroFS 9P port |
version=9p2000.L | Use Linux-specific 9P version |
Performance Options
| Option | Description | Default |
|---|---|---|
msize=N | Maximum message size in bytes | 8192 |
cache=mode | Caching mode (see below) | none |
access=mode | Access check mode | user |
Cache Modes
| Mode | Description | Use Case |
|---|---|---|
none | No caching, direct I/O | Maximum consistency |
loose | Relaxed consistency | Best performance |
fscache | Persistent cache | Cache survives unmount |
mmap | Enable mmap support | Required for memory-mapped file access |
The cache=mmap option doesn't create a cache - it enables support for memory-mapped files. Use this only if your applications use mmap() system calls. For general performance, use cache=loose.
Configuration
Persistent Mount
Add to /etc/fstab:
# Basic persistent mount
127.0.0.1 /mnt/zerofs-9p 9p trans=tcp,port=5564,version=9p2000.L,_netdev 0 0
# With performance options
127.0.0.1 /mnt/zerofs-9p 9p trans=tcp,port=5564,version=9p2000.L,msize=1048576,cache=loose,_netdev 0 0
Systemd Mount Unit
Create /etc/systemd/system/mnt-zerofs-9p.mount:
[Unit]
Description=ZeroFS 9P Mount
After=network.target
[Mount]
What=127.0.0.1
Where=/mnt/zerofs-9p
Type=9p
Options=trans=tcp,port=5564,version=9p2000.L,msize=1048576,cache=loose,_netdev
[Install]
WantedBy=multi-user.target
Enable and start:
sudo systemctl enable mnt-zerofs-9p.mount
sudo systemctl start mnt-zerofs-9p.mount
Performance Tuning
Message Size
Larger message sizes improve throughput for sequential I/O:
# Low (8KB)
-o msize=8192
# Recommended (1MB)
-o msize=1048576
Cache Mode Selection
Choose based on your workload:
# Development - frequent file changes
sudo mount -t 9p -o cache=none ...
# Applications using mmap (databases, etc.)
sudo mount -t 9p -o cache=mmap ...
# Best performance, accept some inconsistency
sudo mount -t 9p -o cache=loose ...
Troubleshooting
Mount Fails
# Check if ZeroFS is running
ps aux | grep zerofs
# Verify 9P port is open
nc -zv 127.0.0.1 5564
# Check kernel modules
lsmod | grep 9p
# Enable debug messages
sudo mount -t 9p -o trans=tcp,port=5564,debug=0x1ff 127.0.0.1 /mnt/test
Performance Issues
# Check current mount options
mount | grep 9p
# Test with different cache modes
for mode in none mmap loose; do
echo "Testing cache=$mode"
sudo umount /mnt/zerofs-9p
sudo mount -t 9p -o cache=$mode,msize=1048576,trans=tcp,port=5564 127.0.0.1 /mnt/zerofs-9p
# Run your benchmark
done
9P vs NFS Comparison
When to Use 9P
- Linux-only environments
- Need maximum performance on Linux
- Simpler protocol overhead is beneficial
- Applications requiring correct fsync behavior (databases, transactional systems)
When to Use NFS
- Cross-platform compatibility needed
- macOS or Windows clients
- Need automatic reconnection on network issues
- Existing NFS infrastructure and tooling
Performance Characteristics
| Aspect | 9P | NFS |
|---|---|---|
| Protocol Overhead | Lower | Higher |
| Linux Performance | Better | Good |
| Cross-Platform | Linux only | Universal |
| fsync Behavior | Correct | Limited* |
*NFS COMMIT semantics may not provide expected durability guarantees for fsync operations
Security Considerations
Like the NFS server, ZeroFS's 9P server has no built-in authentication:
- Bind to localhost only (default behavior)
- Use firewall rules for network access
- Consider SSH tunneling for remote access
- No encryption - use VPN or tunnel for sensitive data
Advanced Usage
Multiple Cache Modes
Mount the same filesystem with different cache modes:
# Consistent mount for important operations
sudo mount -t 9p -o cache=none,trans=tcp,port=5564 127.0.0.1 /mnt/zerofs-consistent
# Performance mount for read-heavy operations
sudo mount -t 9p -o cache=loose,trans=tcp,port=5564 127.0.0.1 /mnt/zerofs-fast