ZFS ARC Statistics Monitoring Script

A Python script to collect and log ZFS Adaptive Replacement Cache (ARC) and L2ARC statistics using the arcstat utility.

Features

• Collects ARC/L2ARC performance metrics at configurable intervals
• Logs data to CSV for long-term monitoring and analysis
• Tracks extended statistics including:
  • L2ARC MRU/MFU percentages
  • MRU/MFU size metrics
  • Ghost cache statistics
  • Hit ratios and cache sizes
• Automatic unit conversion (bytes to GB)
• Configurable sampling parameters

Installation

1. I have a seperate dataset in my pool /mnt/tank/tn_scripts that I use for this purpose, and I highly recommend you should as well.
2. git clone https://github.com/nickf1227/arcstat_collector.git /mnt/tank/tn_scripts Replace the path with where you want to store it on your system, and then run it.
3. You can call the script by running python3 /mnt/tank/tn_scripts/arcstat_collector/arcstat_collector.py

Configuration

Edit these variables in the script:

Configurable settings

SAMPLING_INTERVAL = 10 # arcstat sampling interval in seconds SAMPLING_FREQUENCY = 60 # How often to collect samples in seconds CSV_OUTPUT_PATH = "." # Output directory for CSV file

For now, columns include the below. I plan to expose more later. Please see https://openzfs.github.io/openzfs-docs/man/master/1/arcstat.1.html:

timestamp: Measurement time (YYYY-MM-DD HH:MM:SS )

size (GB): Total ARC size

hit%: ARC hit percentage

l2size (GB): L2ARC device size

l2hit%: L2ARC hit percentage

l2mru%: L2ARC MRU (Most Recently Used) percentage

mrusz%: MRU size percentage

mrugsz (GB): MRU ghost size

l2mfu%: L2ARC MFU (Most Frequently Used) percentage

mfusz%: MFU size percentage

mfugsz (GB): MFU ghost size

Troubleshooting

Common Issues:

Permission Denied for arcstat

Run with sudo: sudo python3 arcstat_monitor.py