Prerequisites

The instructions have been tested on a Raspberry Pi 4 running Debian GNU/Linux 12 (Bookworm) with a disk connected via USB3.

Install packages:

sudo apt update
sudo apt install -y hdparm sysstat bc

Scripts

disk-monitor.sh

Create file /usr/local/bin/disk-monitor.sh:

vi /usr/local/bin/disk-monitor.sh

with body:

#!/bin/bash

# Script for monitoring disk activity on /dev/sda
# If the disk is idle for 60 seconds, it is put into sleep mode

DISK="/dev/sda"
IDLE_TIMEOUT=3600
LAST_ACTIVITY_FILE="/tmp/disk_activity_timestamp"
CHECK_INTERVAL=5

# Log file
LOG_FILE="/var/log/disk-monitor.log"

log_message() {
    echo "$(date '+%Y-%m-%d %H:%M:%S') - $1" >> "$LOG_FILE"
}

# Initialization
log_message "Starting disk monitor for $DISK"

while true; do
    # Check disk activity using iostat
    # Read the number of I/O operations
    CURRENT_IO=$(cat /proc/diskstats | grep -w sda | awk '{print $1}')
    
    # If the last activity file does not exist, create it
    if [ ! -f "$LAST_ACTIVITY_FILE" ]; then
        echo "$(date +%s)" > "$LAST_ACTIVITY_FILE"
        log_message "Timestamp file has been created"
    fi
    
    # Read the latest timestamp
    LAST_TIMESTAMP=$(cat "$LAST_ACTIVITY_FILE")
    CURRENT_TIMESTAMP=$(date +%s)
    TIME_IDLE=$((CURRENT_TIMESTAMP - LAST_TIMESTAMP))
    
    # Check if the disk is active
    # Use iostat to verify actual activity
    if command -v iostat &> /dev/null; then
        # Check using iostat
        IO_PERCENT=$(iostat -x 1 2 | grep sda | tail -1 | awk '{print $4}')
        if (( $(echo "$IO_PERCENT > 0" | bc -l) )); then
            echo "$(date +%s)" > "$LAST_ACTIVITY_FILE"
            log_message "Disk activity detected - IO: $IO_PERCENT%"
        fi
    else
        # Fallback – if iostat is not available, check /proc/diskstats
        CURRENT_READS=$(cat /proc/diskstats | grep -w sda | awk '{print $4}')
        LAST_READS=$(cat "$LAST_ACTIVITY_FILE.reads" 2>/dev/null || echo "0")
        
        if [ "$CURRENT_READS" != "$LAST_READS" ]; then
            echo "$(date +%s)" > "$LAST_ACTIVITY_FILE"
            echo "$CURRENT_READS" > "$LAST_ACTIVITY_FILE.reads"
            log_message "Disk activity detected - odczyty: $CURRENT_READS"
        else
            echo "$CURRENT_READS" > "$LAST_ACTIVITY_FILE.reads"
        fi
    fi
    
    # Updating inactivity timeout
    LAST_TIMESTAMP=$(cat "$LAST_ACTIVITY_FILE")
    CURRENT_TIMESTAMP=$(date +%s)
    TIME_IDLE=$((CURRENT_TIMESTAMP - LAST_TIMESTAMP))
    
    # If the disk is idle for IDLE_TIMEOUT seconds
    if [ $TIME_IDLE -ge $IDLE_TIMEOUT ]; then
        log_message "Drive idle for $TIME_IDLE seconds – entering sleep mode"
        sudo hdparm -Y /dev/sda 2>> "$LOG_FILE"
        
        if [ $? -eq 0 ]; then
            log_message "Disk $DISK successfully spun down"
            rm -f "$LAST_ACTIVITY_FILE"
        else
            log_message "ERROR: Failed to spin down disk $DISK"
        fi
    fi
    
    sleep $CHECK_INTERVAL
done

Two important parameters that must be configured for your disk:

• DISK="/dev/sda" - specify the HDD disk to be checked and stopped
• IDLE_TIMEOUT=3600 - time in seconds after which it will be stopped due to inactivity

Add execution permissions:

sudo chmod +x /usr/local/bin/disk-monitor.sh

disk-monitor.service

Create file disk-monitor.service:

sudo vi /etc/systemd/system/disk-monitor.service

with body:

[Unit]
Description=HDD activity monitor and sleep service
After=network.target
StartLimitIntervalSec=60
StartLimitBurst=3

[Service]
Type=simple
User=root
ExecStart=/usr/local/bin/disk-monitor.sh
Restart=on-failure
RestartSec=10
StandardOutput=journal
StandardError=journal
SyslogIdentifier=disk-monitor
TimeoutStopSec=10

[Install]
WantedBy=multi-user.target

Add execution permissions:

sudo chmod 644 /etc/systemd/system/disk-monitor.service

Enable and start the service:
```bash
sudo systemctl daemon-reload
sudo systemctl enable disk-monitor.service
sudo systemctl start disk-monitor.service

Problems

In case of problems, check using the following command whether the disk is stopping programmatically:

sudo hdparm -Y /dev/sda