13 - USB Disk Troubleshooting

Date: 2026-02-09
System: Proxmox VE 8
Affected device: ADATA HD710 PRO 1.8TB (USB 3.0 external hard drive)

Problem Description¶

The /mnt/disk4 mountpoint was randomly unmounting, causing the following issues: - Jellyfin media server was unable to play files - MergerFS pool became partially inaccessible - Netdata generated false alarm alerts

Symptoms¶

[Thu Feb 5 08:45:43 2026] usb 2-9: USB disconnect, device number 3
[Thu Feb 5 08:45:43 2026] device offline error, dev sdd
[Thu Feb 5 08:45:43 2026] EXT4-fs (sdd1): shut down requested (2)
[Thu Feb 5 08:45:43 2026] EXT4-fs (sdd1): unmounting filesystem

Root Cause Analysis¶

Hardware Info¶

Device: ADATA HD710 PRO
Connection: USB 3.0 (Bus 002, Device variable)
Vendor ID: 125f
Product ID: a75a
Serial: YOUR_USB_SERIAL
Capacity: 1.8TB (1,950,615,552 sectors)

Root Cause¶

The USB device automatically entered suspend mode (Linux USB power management), which caused a disconnect event. The EXT4 filesystem performed an emergency shutdown as a protective measure.

Implemented Solutions¶

1. Disable USB Autosuspend¶

File: /etc/udev/rules.d/50-adata-no-suspend.rules

# ADATA HD710 PRO - disable USB autosuspend
ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="125f", ATTR{idProduct}=="a75a", TEST=="power/control", ATTR{power/control}="on"
ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="125f", ATTR{idProduct}=="a75a", TEST=="power/autosuspend", ATTR{power/autosuspend}="-1"

Apply:

udevadm control --reload-rules
echo on > /sys/bus/usb/devices/2-9/power/control
echo -1 > /sys/bus/usb/devices/2-9/power/autosuspend

2. Automatic Remount Watchdog¶

File: /usr/local/bin/disk4-watchdog.sh

#!/bin/bash
while true; do
    if ! mountpoint -q /mnt/disk4; then
        logger "disk4-watchdog: /mnt/disk4 not mounted, attempting remount..."
        mount /mnt/disk4 && logger "disk4-watchdog: Successfully remounted /mnt/disk4"
    fi
    sleep 60
done

Systemd Service: /etc/systemd/system/disk4-watchdog.service

[Unit]
Description=Disk4 Auto-remount Watchdog
After=local-fs.target

[Service]
Type=simple
ExecStart=/usr/local/bin/disk4-watchdog.sh
Restart=always

[Install]
WantedBy=multi-user.target

Activate:

chmod +x /usr/local/bin/disk4-watchdog.sh
systemctl daemon-reload
systemctl enable disk4-watchdog
systemctl start disk4-watchdog

System Configuration¶

/etc/fstab - Disk Mounts¶

# 2x 6TB HDD mounts
UUID=YOUR_DISK1_UUID  /mnt/disk1  ext4  defaults,noatime  0  2
UUID=YOUR_DISK2_UUID  /mnt/disk2  ext4  defaults,noatime  0  2

# USB HDDs
UUID=YOUR_DISK3_UUID  /mnt/disk3  ext4  defaults,noatime  0  2
UUID=YOUR_DISK4_UUID  /mnt/disk4  ext4  defaults,noatime  0  2

# MergerFS (disk2 is SnapRAID parity, not in pool!)
/mnt/disk1:/mnt/disk3:/mnt/disk4  /mnt/storage  fuse.mergerfs  defaults,allow_other,use_ino,cache.files=partial,dropcacheonclose=true,category.create=mfs  0  0

Disk Layout¶

Disk	Size	Type	Mount Point	Role
sda1	5.5TB	SATA	/mnt/disk1	Data + MergerFS
sdb1	5.5TB	SATA	/mnt/disk2	SnapRAID Parity
sdc1	931GB	SATA	/mnt/disk3	Data + MergerFS
sdd1	1.8TB	USB 3.0	/mnt/disk4	Data + MergerFS

Total MergerFS pool: ~8.1TB

Verification Commands¶

Watchdog Status¶

systemctl status disk4-watchdog
journalctl -u disk4-watchdog -f

USB Power Settings¶

cat /sys/bus/usb/devices/2-9/power/control      # Output: on
cat /sys/bus/usb/devices/2-9/power/autosuspend  # Output: -1

Disk Mount Status¶

lsblk | grep sdd
mount | grep disk4
df -h | grep disk4

MergerFS Status¶

mount | grep storage
df -h | grep storage
ls /mnt/storage/media  # Test whether it is accessible

USB Disconnect Monitoring (real-time)¶

dmesg -w | grep -i "usb\|sdd"

Troubleshooting¶

If disk4 unmounts AGAIN:¶

Check watchdog operation:

   systemctl status disk4-watchdog
   journalctl -u disk4-watchdog --since "10 minutes ago"

Check kernel logs:

   dmesg -T | grep -i "sdd\|usb" | tail -50

Manual remount:
```
   mount /mnt/disk4
```
If the watchdog does NOT remount automatically:
```
   systemctl restart disk4-watchdog
```

If problems persist:¶

Hardware solutions: 1. Try a different USB port (rear port > front port) 2. Use a shorter or better quality USB 3.0 cable 3. Use an externally powered USB hub if available 4. Check that too many devices are not sharing the same USB controller

Additional software settings:

# Increase Linux kernel USB timeout (optional, if disconnects still occur)
echo 0 > /sys/module/usbcore/parameters/autosuspend

SMART Monitoring¶

Regular health checks for the disk:

# Quick health check
smartctl -H /dev/sdd

# Detailed info
smartctl -a /dev/sdd

# Run extended test (offline, ~2-3 hours)
smartctl -t long /dev/sdd

SMART Status (last check): PASSED ✅

Next Steps¶

✅ USB autosuspend disabled
✅ Watchdog service running and enabled
⏳ Monitor for 1-2 weeks to see if the problem recurs
🔜 If stable → close documentation
🔜 If not → hardware replacement (cable/hub/port)

Jellyfin Docker¶

If Jellyfin stops working after a disk unmount:

cd /srv/docker-data/jellyfin
docker-compose restart
docker logs jellyfin --tail 50

MergerFS Reload¶

If the MergerFS pool does not refresh:

umount /mnt/storage
mount /mnt/storage

Notes¶

disk2 is NOT part of the MergerFS pool because it is the SnapRAID parity disk
The watchdog checks the mount every 60 seconds
The USB device is on port 2-9, which may change on reconnect
The udev rules apply automatically after every boot

Last updated: 2026-02-09
Status: Resolved, under observation
Author: Nex @ Proxmox homelab