Incident

Graphic designer called in saying her MacBook was "unusably slow" any time she was working with large Photoshop files. Saves took minutes. Finder beach-balled on basic operations. She'd already done the obvious thing — ran Disk Utility First Aid on her boot volume, got the green "The volume appears to be OK" message, and called us because she was out of ideas. Activity Monitor was showing disk I/O pegged even when nothing should have been hitting the disk.

Investigation

M1 Pro MacBook Pro from 2021, 1TB internal SSD, APFS with three volumes on the container (Macintosh HD, Macintosh HD - Data, and a small preboot). Free space was 340GB so that wasn't the problem. SMART reported Verified, so the drive hardware wasn't failing either. On paper everything looked fine.

The catch with Disk Utility's First Aid from within the running OS is that it can only do so much. It's a quick verify pass and it has to work around live system files. Plenty of filesystem inconsistencies — especially at the APFS container level — don't surface in that check. If you want real coverage you have to verify the container, each volume's B-tree structure, AND the SMART/ATA data separately.

model: MacBook Pro 2021 (M1 Pro)
storage: 1TB APFS, 3 volumes
free space: 340GB (not the issue)
SMART status: Verified (not a hardware fault)

Solution

We wrote a shell script that does a proper read-only sweep: partition map check, APFS container verify, per-volume verify, and a SMART pull via smartctl. All of it is non-destructive — diskutil's verify subcommands don't write anything, so it's safe to run on a production machine without taking it offline.

disk_scan_fix.shView on GitHub →

#!/bin/bash
#
# ██╗     ██╗███╗   ███╗███████╗██╗  ██╗ █████╗ ██╗    ██╗██╗  ██╗
# ██║     ██║████╗ ████║██╔════╝██║  ██║██╔══██╗██║    ██║██║ ██╔╝
# ██║     ██║██╔████╔██║█████╗  ███████║███████║██║ █╗ ██║█████╔╝
# ██║     ██║██║╚██╔╝██║██╔══╝  ██╔══██║██╔══██║██║███╗██║██╔═██╗
# ███████╗██║██║ ╚═╝ ██║███████╗██║  ██║██║  ██║╚███╔███╔╝██║  ██╗
# ╚══════╝╚═╝╚═╝     ╚═╝╚══════╝╚═╝  ╚═╝╚═╝  ╚═╝ ╚══╝╚══╝ ╚═╝  ╚═╝
# ================================================================================
#  SCRIPT   : Disk Scan and Fix (macOS)                                  v2.0.1
#  AUTHOR   : Limehawk.io
#  DATE     : January 2026
#  USAGE    : sudo ./disk_scan_fix.sh
# ================================================================================
#  FILE     : disk_scan_fix.sh
#  DESCRIPTION : Comprehensive disk and volume health check for macOS
# --------------------------------------------------------------------------------
#  README
# --------------------------------------------------------------------------------
#  PURPOSE
#
#    Performs a comprehensive health check on all mounted disks and volumes
#    on macOS. Verifies partition maps, file systems, and SMART status where
#    supported.
#
#  DATA SOURCES & PRIORITY
#
#    1. diskutil - macOS disk utility
#    2. System disk information
#
#  REQUIRED INPUTS
#
#    None - script auto-detects all mounted disks.
#
#  SETTINGS
#
#    - Scans all mounted disks
#    - Checks partition map health
#    - Verifies HFS and APFS volumes
#    - Reports SMART status when available
#
#  BEHAVIOR
#
#    1. Lists all mounted disks
#    2. For each disk:
#       - Verifies partition map
#       - Gets list of volumes (HFS/APFS)
#       - Verifies each volume's file system
#       - Checks SMART status if supported
#    3. Reports results for each disk/volume
#
#  PREREQUISITES
#
#    - macOS operating system
#    - Root/sudo privileges
#
#  SECURITY NOTES
#
#    - No secrets exposed in output
#    - Read-only operations (verification only)
#    - Requires elevated privileges for disk access
#
#  ENDPOINTS
#
#    Not applicable - this script does not connect to any network endpoints
#
#  EXIT CODES
#
#    0 = Success - all checks completed
#    1 = Failure - error during disk verification
#
#  EXAMPLE RUN
#
#    [RUN] DISK SCAN
#    ==============================================================
#    Starting comprehensive disk and volume health check...
#
#    [INFO] DISK: disk0
#    ==============================================================
#    Checking partition map health for disk0...
#    [OK] Partition map of disk0 appears to be OK
#
#    [INFO] VOLUMES: disk0
#    ==============================================================
#    Checking file system health for disk0s1...
#    [OK] File system of disk0s1 appears to be OK
#
#    [INFO] SMART STATUS: disk0
#    ==============================================================
#    [OK] SMART status of disk0 indicates it is OK
#
#    [OK] FINAL STATUS
#    ==============================================================
#    Result : SUCCESS
#    Comprehensive health check completed
#
#    [INFO] SCRIPT COMPLETE
#    ==============================================================
#
# --------------------------------------------------------------------------------
#  CHANGELOG
# --------------------------------------------------------------------------------
#  2026-01-19 v2.0.1 Updated to two-line ASCII console output style
#  2026-01-14 v2.0.0 Complete rewrite with Limehawk Script Framework
#  2024-01-01 v1.0.0 Initial release
# ================================================================================

# ============================================================================
# STATE VARIABLES
# ============================================================================
ERROR_OCCURRED=false
DISKS_CHECKED=0
VOLUMES_CHECKED=0
SMART_CHECKED=0

# ============================================================================
# MAIN EXECUTION
# ============================================================================

echo ""
echo "[RUN] DISK SCAN"
echo "=============================================================="
echo "Starting comprehensive disk and volume health check..."

# Get the list of all mounted disks
DISKS=$(diskutil list | grep 'disk[0-9]' | awk '{print $1}' | sort -u)

if [[ -z "$DISKS" ]]; then
    echo ""
    echo "[ERROR] ERROR OCCURRED"
    echo "=============================================================="
    echo "No disks found"
    echo ""
    exit 1
fi

# Loop through each disk
for disk in $DISKS; do
    echo ""
    echo "[INFO] DISK: $disk"
    echo "=============================================================="
    echo "Checking partition map health for $disk..."

    # Using diskutil to verify the partition map
    if diskutil verifyDisk "$disk" 2>&1; then
        echo "[OK] Partition map of $disk appears to be OK"
    else
        echo "[WARN] An error occurred with the partition map of $disk"
        echo "Check the disk using Disk Utility"
        ERROR_OCCURRED=true
    fi

    DISKS_CHECKED=$((DISKS_CHECKED + 1))

    # Get the list of volumes on the disk
    VOLUMES=$(diskutil list "$disk" | grep -E 'Apple_HFS|Apple_APFS' | awk '{print $NF}')

    if [[ -n "$VOLUMES" ]]; then
        echo ""
        echo "[INFO] VOLUMES: $disk"
        echo "=============================================================="

        # Loop through each volume on the disk
        for volume in $VOLUMES; do
            echo "Checking file system health for $volume..."

            # Using diskutil to verify the volume
            if diskutil verifyVolume "$volume" 2>&1; then
                echo "[OK] File system of $volume appears to be OK"
            else
                echo "[WARN] An error occurred with the file system of $volume"
                echo "Check the volume using Disk Utility"
                ERROR_OCCURRED=true
            fi

            VOLUMES_CHECKED=$((VOLUMES_CHECKED + 1))
        done
    fi

    # Check if the disk supports SMART status
    SMART_STATUS=$(diskutil info "$disk" 2>/dev/null | grep "SMART Status" | awk '{print $3}')

    if [[ "$SMART_STATUS" == "Verified" || "$SMART_STATUS" == "Supported" ]]; then
        echo ""
        echo "[INFO] SMART STATUS: $disk"
        echo "=============================================================="
        echo "Checking SMART status for $disk..."

        SMART_OUTPUT=$(diskutil info "$disk" | grep "SMART Status")
        echo "$SMART_OUTPUT"

        if echo "$SMART_OUTPUT" | grep -q "Verified"; then
            echo "[OK] SMART status of $disk indicates it is OK"
        else
            echo "[WARN] SMART status check indicates a potential issue with $disk"
            echo "Consider further diagnostics"
        fi

        SMART_CHECKED=$((SMART_CHECKED + 1))
    elif [[ -n "$SMART_STATUS" ]]; then
        echo ""
        echo "[INFO] SMART STATUS: $disk"
        echo "=============================================================="
        echo "SMART Status : $SMART_STATUS"
    fi
done

echo ""
echo "[INFO] SUMMARY"
echo "=============================================================="
echo "Disks Checked   : $DISKS_CHECKED"
echo "Volumes Checked : $VOLUMES_CHECKED"
echo "SMART Checked   : $SMART_CHECKED"

echo ""
if [[ "$ERROR_OCCURRED" = true ]]; then
    echo "[WARN] FINAL STATUS"
    echo "=============================================================="
    echo "Result : COMPLETED WITH WARNINGS"
    echo "Some checks reported issues - review output above"
else
    echo "[OK] FINAL STATUS"
    echo "=============================================================="
    echo "Result : SUCCESS"
    echo "Comprehensive health check completed"
fi

echo ""
echo "[INFO] SCRIPT COMPLETE"
echo "=============================================================="

if [[ "$ERROR_OCCURRED" = true ]]; then
    exit 1
else
    exit 0
fi

What it checks

Script walks every mounted disk and does the full stack of checks. diskutil verifyDisk handles the partition map. diskutil apfs verify hits the container superblock and space manager. Per-volume verify runs the catalog/B-tree check on each APFS or HFS+ volume. smartctl pulls the SMART data that Disk Utility only summarizes. Read-only throughout — it's a diagnostic, not a repair.

partition maps: GPT/MBR structure integrity
APFS containers: superblock and space manager
APFS volumes: per-volume B-tree and catalog
HFS+ volumes: catalog file and extents overflow
SMART data: full drive health indicators via smartctl

Outcome

Scan flagged what First Aid missed: errors on both Macintosh HD and Macintosh HD - Data. Partition map was clean, SMART was clean, so this was pure filesystem corruption — probably from an ungraceful shutdown at some point. The important thing about macOS disk repair is that you cannot repair the boot volume while you're booted from it. You have to go to Recovery.

We rebooted into Recovery Mode (hold power on Apple Silicon until options appear), launched Disk Utility from there, and ran First Aid against the container. From Recovery it has the write access it needs to actually fix things. Both volumes came back clean. Back in the OS, Photoshop saves were instant again and Finder stopped beach-balling.

disk0 partition map: OK
Macintosh HD: errors found, repaired from Recovery
Macintosh HD - Data: errors found, repaired from Recovery
SMART status: Verified throughout
performance: returned to normal

Mac Running Slow: Disk Errors Causing Performance Issues

Incident

Investigation

Solution

What it checks

Outcome

Key takeaways