**License: Free** - No license required. Available in all tiers.

LogicalDisk Probe#

The LogicalDisk probe monitors disk and filesystem performance across all major operating systems, providing comprehensive metrics for capacity, I/O operations, throughput, and filesystem health.

Quick Start#

Basic Configuration#

probes:
  - name: logicaldisk
    params:
      interval: 30  # Collection interval in seconds (default: 30)

Minimal Configuration#

probes:
  - name: logicaldisk
    params: {}

The LogicalDisk probe requires no mandatory parameters and works out-of-the-box with default settings.

Supported Platforms#

• Windows: Windows Server 2012+ / Windows 10+
• Linux: All modern distributions (Ubuntu, RHEL, CentOS, Debian, etc.)
• macOS: macOS 10.13+
• BSD: FreeBSD, OpenBSD, NetBSD

Platform-specific metrics are automatically detected and collected based on the operating system.

Key Metrics Summary#

Cross-Platform Capacity Metrics#

Cross-Platform I/O Metrics#

Unix/Linux/macOS Specific#

Configuration Parameters#

Example Configurations#

High-frequency monitoring (every 10 seconds):

probes:
  - name: logicaldisk
    params:
      interval: 10

Standard monitoring (every minute):

probes:
  - name: logicaldisk
    params:
      interval: 60

Windows: Monitor specific drives only:

probes:
  - name: logicaldisk
    params:
      interval: 30
      filters:
        include: ["C:", "D:", "E:"]
        exclude: ["HarddiskVolume*", "_Total"]

Windows: Exclude drives matching patterns:

probes:
  - name: logicaldisk
    params:
      interval: 30
      filters:
        exclude: ["HarddiskVolume*", "_Total", "X:", "Y:"]

Monitoring Tool Integration#

PRTG Network Monitor#

Access LogicalDisk metrics in PRTG JSON format:

# All disk metrics
curl http://localhost:8080/api/{agentkey}/prtg/metrics

# Configure PRTG HTTP Advanced Sensor:
# - URL: http://agent-host:8080/api/{agentkey}/prtg/metrics
# - Method: POST
# - Request body: {"probe": "logicaldisk"}

PRTG Channels Available:

• Disk Free Space (MB or %)
• Disk IOPS (reads/writes per second)
• Disk Throughput (read/write bytes per second)
• Disk Queue Length
• Filesystem Usage (bytes and %)
• Inode Usage (Unix/Linux)

Nagios/Icinga#

Access LogicalDisk metrics in Nagios format:

# All disk metrics with performance data
curl http://localhost:8080/api/{agentkey}/nagios/metrics?probe=logicaldisk

# Example output:
# OK - Disk monitoring active | disk_free_percent_C:=45.2%;10;5 disk_queue_length=0.8;;;

Nagios Performance Data:

• disk_free_percent - Free space percentage with 10% warning, 5% critical
• fs_used_percent - Used space percentage (Unix)
• disk_queue_length - Disk queue depth (Windows)
• fs_inodes_used_percent - Inode usage (Unix)

Grafana/Prometheus#

Access metrics in Prometheus-compatible format:

# Prometheus format
curl http://localhost:8080/api/{agentkey}/prometheus/metrics

# Example output:
# disk_free_percent{hostname="server01",drive="C:"} 45.2
# disk_reads_sec{hostname="server01",drive="C:"} 123.4
# fs_used_percent{hostname="server01",mount_point="/",device="/dev/sda1"} 67.8

Web Interface#

View LogicalDisk metrics in the built-in dashboard:

http://localhost:8080/web/{agentkey}/dashboard

Features:

• Real-time disk usage visualization
• Per-disk/mount point breakdown
• I/O throughput graphs
• Capacity trend analysis

Use Cases#

Capacity Planning#

Monitor disk space to prevent:

• Out-of-disk-space incidents
• Application failures due to full disks
• Database transaction log issues
• Backup failures

Key Metrics:

• disk_free_percent / fs_used_percent
• fs_inodes_used_percent (Unix/Linux)

Alert Thresholds:

• Warning: < 20% free
• Critical: < 10% free
• Inode Warning: > 80% used

I/O Bottleneck Detection#

Identify storage performance issues:

• Slow disk I/O
• High queue depths
• Excessive IOPS
• Throughput saturation

Key Metrics:

• disk_queue_length (Windows)
• disk_reads_sec / disk_writes_sec
• disk_read_bytes_sec / disk_write_bytes_sec

Alert Thresholds:

• Queue Length: > 2 sustained
• IOPS: Depends on disk type (HDD: ~200, SSD: ~10000)

Filesystem Health Monitoring#

Track filesystem integrity and performance:

• Inode exhaustion (Unix/Linux)
• Filesystem type optimization
• Mount point availability
• Storage subsystem health

Key Metrics:

• fs_inodes_used_percent (Unix/Linux)
• Availability of expected mount points
• Filesystem type distribution

Application-Specific Monitoring#

Monitor critical application storage:

• Database data and log volumes
• Application temp directories
• Cache directories
• User data volumes

Implementation:

• Use drive/mount_point tags for filtering
• Set application-specific thresholds
• Correlate with application metrics

Platform-Specific Behavior#

Windows#

Collection Method:

• Uses Performance Data Helper (PDH) counters
• Monitors LogicalDisk performance object
• Real-time per-drive metrics

Drive Identification:

• Drive letters: C:, D:, E:, etc.
• Tag: drive=C:

Default Filters:

• Includes: All drives (empty = all)
• Excludes: HarddiskVolume* (system volumes), _Total (aggregate)

Example Metrics:

disk_free_mb{drive="C:"} = 102400
disk_free_percent{drive="C:"} = 45.2
disk_reads_sec{drive="C:"} = 123.4
disk_writes_sec{drive="C:"} = 87.6
disk_read_bytes_sec{drive="C:"} = 5242880
disk_write_bytes_sec{drive="C:"} = 3145728
disk_queue_length{drive="C:"} = 0.8

Unix/Linux#

Collection Method:

• Uses /proc/mounts for filesystem discovery
• syscall.Statfs for capacity metrics
• Filters pseudo-filesystems automatically

Filesystem Type Filtering:

• Included: ext4, ext3, ext2, xfs, vfat, fuse
• Excluded: sysfs, proc, devpts, overlay, squashfs, etc.
• tmpfs: Only specific mounts (/run, /dev/shm, /run/lock)

Mount Point Identification:

• Full mount path: /, /home, /var, etc.
• Tags: mount_point=/home, fs_type=ext4, device=/dev/sda1

Example Metrics:

fs_total_bytes{mount_point="/",device="/dev/sda1",fs_type="ext4"} = 107374182400
fs_free_bytes{mount_point="/",device="/dev/sda1",fs_type="ext4"} = 48318382080
fs_used_bytes{mount_point="/",device="/dev/sda1",fs_type="ext4"} = 59055800320
fs_available_bytes{mount_point="/",device="/dev/sda1",fs_type="ext4"} = 45318382080
fs_used_percent{mount_point="/",device="/dev/sda1",fs_type="ext4"} = 55.0
fs_inodes_total{mount_point="/",device="/dev/sda1",fs_type="ext4"} = 6553600
fs_inodes_free{mount_point="/",device="/dev/sda1",fs_type="ext4"} = 5242880
fs_inodes_used{mount_point="/",device="/dev/sda1",fs_type="ext4"} = 1310720
fs_inodes_used_percent{mount_point="/",device="/dev/sda1",fs_type="ext4"} = 20.0

macOS#

Collection Method:

• Uses df -h command for filesystem discovery
• syscall.Statfs for capacity metrics
• APFS-specific handling with automatic whitelist inclusion

Filesystem Type Detection:

• APFS: Modern macOS filesystem for volumes starting with /dev/disk* (automatically included)
• Excludes: devfs, autofs, system volumes

APFS Support: The LogicalDisk probe automatically recognizes and monitors APFS filesystems on macOS. APFS (Apple File System) is the default filesystem for macOS 10.13+ and includes:

• Container-based storage with shared space pools
• Multiple volumes within a single container
• Snapshot and cloning capabilities
• Strong encryption support

All APFS volumes are included in the standardFS whitelist for automatic monitoring.

Mount Point Filtering:

• Included: /, /System/Volumes/Data, /Volumes/*, APFS volumes
• Excluded: /dev, /System/Volumes/Preboot, /System/Volumes/VM, /System/Volumes/Update

Example Metrics:

fs_total_bytes{mount_point="/",device="/dev/disk1s1",fs_type="apfs"} = 250685575168
fs_free_bytes{mount_point="/",device="/dev/disk1s1",fs_type="apfs"} = 123456789120
fs_used_percent{mount_point="/",device="/dev/disk1s1",fs_type="apfs"} = 50.7
fs_inodes_total{mount_point="/",device="/dev/disk1s1",fs_type="apfs"} = 9223372036854775807
fs_inodes_used_percent{mount_point="/",device="/dev/disk1s1",fs_type="apfs"} = 0.01

Note: APFS uses a dynamic inode allocation model, so inode metrics may show very large totals.

Troubleshooting#

No Metrics Collected#

Check probe status:

# View agent logs with LogicalDisk probe debugging
./agent run --authentication-key YOUR_KEY --verbose --debug-modules probe.logicaldisk

Verify probe is enabled:

# Check configuration
cat agent-config.yaml | grep -A5 "name: logicaldisk"

Windows: PDH Counter Errors#

Symptom: Error messages about Performance Data Helper (PDH) counters

Solution:

1. Verify Performance Counter service is running:

   Get-Service | Where-Object {$_.Name -eq "PerfHost"}

2. Rebuild Performance Counters:

   lodctr /R

3. Check Windows Event Log for PDH errors

Unix/Linux: Permission Denied#

Symptom: Cannot read /proc/mounts or perform statfs() calls

Solution: Run the agent with appropriate permissions:

# Option 1: Run as root
sudo ./agent run --authentication-key YOUR_KEY

# Option 2: Grant capabilities (Linux)
sudo setcap cap_sys_ptrace=eip ./agent

Windows: Drives Not Appearing#

Symptom: Expected drives missing from metrics

Possible Causes:

1. Drive filtered out: Check filters.exclude configuration
2. System volume: HarddiskVolume* excluded by default
3. Network drive: May not appear in LogicalDisk counters

Solution:

probes:
  - name: logicaldisk
    params:
      filters:
        include: ["C:", "D:", "E:", "Z:"]  # Explicitly include network drive
        exclude: ["_Total"]  # Keep minimal exclusions

Unix/Linux: Filesystems Not Appearing#

Symptom: Expected mount points missing from metrics

Possible Causes:

1. Filesystem type excluded: Check shouldCollectMount() logic
2. tmpfs mount not in allowed list: Only specific tmpfs mounts included
3. Pseudo-filesystem: sysfs, proc, devpts, etc. are excluded

Debug:

# List all mount points
cat /proc/mounts

# Check which filesystems are collected
./agent run --authentication-key YOUR_KEY --verbose --debug-modules probe.logicaldisk

Solution (if needed): Modify configuration to include specific mount points or filesystem types (requires code modification for custom filters).

Inode Exhaustion Not Detected#

Symptom: Disk has space but applications fail (Unix/Linux)

Cause: Inode exhaustion (many small files)

Solution: Monitor fs_inodes_used_percent metric:

# Check inode usage manually
df -i

# Set alerts on inode usage
# Alert if fs_inodes_used_percent > 80%

Disk Queue Length Always Zero#

Symptom: disk_queue_length metric shows 0 even under load (Windows)

Possible Causes:

1. Disk not busy: Normal behavior for idle disks
2. SSD with high IOPS: Queue empties too quickly to observe
3. Counter issue: PDH counter not updating

Debug:

# Check queue length in Performance Monitor
typeperf "\LogicalDisk(C:)\Current Disk Queue Length" -sc 10

Performance Considerations#

Collection Overhead#

The LogicalDisk probe has minimal overhead:

• Windows: ~50ms per collection (PDH counters)
• Unix/Linux: ~100ms per collection (filesystem syscalls)
• macOS: ~150ms per collection (df command + syscalls)

Memory Usage#

Typical memory footprint per collection:

• Base probe: ~200 KB
• Per-drive/mount metrics: ~100 KB per filesystem
• Example: 5 drives/mounts = ~700 KB total

Recommended Intervals#

Note: I/O metrics (IOPS, throughput, queue) benefit from shorter intervals. Capacity metrics can use longer intervals.

Advanced Configuration#

Multi-Instance Monitoring#

Monitor with different intervals for capacity vs. I/O:

probes:
  - name: logicaldisk_capacity
    params:
      interval: 300  # Check capacity every 5 minutes

  - name: logicaldisk_io
    params:
      interval: 30  # Check I/O every 30 seconds

Note: This will create duplicate metrics. Use unique probe names for different collection intervals.

Integration with Other Probes#

Correlate disk metrics with system metrics:

probes:
  - name: cpu
    params:
      interval: 30

  - name: memory
    params:
      interval: 30

  - name: logicaldisk
    params:
      interval: 30

This provides comprehensive system monitoring:

• High CPU I/O wait + high disk queue = disk bottleneck
• High memory usage + high disk I/O = swapping/paging
• Low disk free + application errors = capacity issue

Windows Drive Letter Filtering#

Scenario: Monitor only production data drives

probes:
  - name: logicaldisk
    params:
      interval: 30
      filters:
        include: ["D:", "E:", "F:"]  # Only data drives
        exclude: ["_Total"]

Scenario: Exclude temporary/cache drives

probes:
  - name: logicaldisk
    params:
      interval: 30
      filters:
        exclude: ["HarddiskVolume*", "_Total", "T:", "X:"]

Unix/Linux Filesystem Filtering#

Note: Unix/Linux filesystem filtering is built-in and automatic. To customize:

1. Include standard filesystems: ext4, ext3, xfs, vfat (automatic)
2. Exclude pseudo-filesystems: sysfs, proc, overlay (automatic)
3. Custom tmpfs mounts: Modify allowedTmpfsMounts in code

Typical Use Cases:

• Monitor root filesystem: / (automatic)
• Monitor data volumes: /data, /var, /home (automatic)
• Monitor external mounts: /mnt/* (depends on fs_type)

Authentication#

The LogicalDisk probe requires no authentication as it collects local system metrics only.

Requirements#

Windows#

• Windows Server 2012+ or Windows 10+
• Performance Counter service enabled
• No special permissions required (runs as service account)

Linux/Unix/macOS#

• Read access to /proc/mounts (Linux)
• syscall.Statfs permissions (standard user)
• df command available (macOS)

Network#

• No network access required (local metrics only)
• HTTP strategy required for remote access to metrics