Resolving SCSI Timeouts In HassOS Preventing Read-Only File System Errors

Jul 17, 2025 by Jeany 74 views

SCSI Timeouts Causing FS to Be Remounted as ReadOnly: A Comprehensive Guide and Solution

Introduction

SCSI timeouts can be a significant issue for systems running Home Assistant Operating System (HassOS) as a virtual machine, particularly those experiencing high I/O loads. This article delves into the problem of SCSI timeouts leading to the file system being remounted as read-only, which can cause system instability and data loss. We will explore the root causes, symptoms, and, most importantly, a practical solution to mitigate this issue. This guide is tailored for users of Home Assistant, system administrators, and anyone managing virtualized environments where SCSI devices are heavily utilized. Ensuring the stability and reliability of your Home Assistant setup is crucial, and understanding how to address SCSI timeouts is a key step in achieving this.

Understanding the Issue

The core problem arises when the Hypervisor, the software that manages virtual machines, experiences high load. This load can delay the processing of SCSI commands, which are used for communication between the virtual machine and the storage device. When these commands take longer than the default timeout period, the system interprets this as an error and remounts the file system as read-only to prevent data corruption. This read-only state effectively freezes the system, making it unresponsive and requiring a reboot. This situation is particularly prevalent during I/O intensive operations such as backups, where large amounts of data are being read from or written to the storage device. Recognizing the conditions that trigger these timeouts is the first step in preventing them. High hypervisor load combined with frequent read/write operations creates a perfect storm for SCSI timeout issues, highlighting the importance of monitoring system performance and proactively addressing potential bottlenecks.

Symptoms and Impact

The symptoms of this issue are quite severe and can significantly disrupt your Home Assistant setup. The most noticeable symptom is the system becoming unresponsive. All processes within the virtual machine effectively freeze, and you will likely be unable to interact with Home Assistant through its web interface or other means. The file system being remounted as read-only is a critical failure that prevents any further writes to the disk. This means that any running processes that attempt to write data, such as logging or updating state information, will fail. This can lead to data loss and system instability. Additionally, the system logs often become inaccessible because the logging mechanism itself relies on writing to the file system. When attempting to access the console, users may be inundated with error messages related to the read-only file system, such as systemd-journald [115] failed to write entry xx items, xxx bytes), ignoring: Read-only file system. These errors are a clear indication that the system is struggling to operate due to the file system constraints. The need for a reboot to restore functionality is a significant inconvenience, especially if the issue occurs frequently. This interruption can also lead to longer-term problems if critical data is lost or corrupted during the forced shutdown.

Root Cause Analysis

The root cause of the problem lies in the default SCSI timeout settings combined with the load on the Hypervisor. The default timeout value, often set at 30 seconds, may be insufficient when the Hypervisor is under heavy load. This is because the Hypervisor's performance can be impacted by various factors, such as CPU utilization, memory pressure, and network activity. When the Hypervisor is busy, it may take longer to process SCSI commands, leading to timeouts. The storage subsystem's ability to handle I/O requests promptly is critical for maintaining system stability. If the virtual machine's requests to the storage device are not acknowledged within the timeout period, the operating system assumes there is a problem with the storage and takes the protective measure of remounting the file system as read-only. This action prevents potential data corruption but also brings the system to a halt. Understanding this interplay between Hypervisor load and SCSI timeouts is essential for implementing effective solutions. Monitoring the Hypervisor's performance and identifying periods of high load can help anticipate and prevent these issues.

Diagnosing the Issue

Diagnosing SCSI timeout issues requires a multi-faceted approach. One of the first indicators is the system's unresponsiveness and the inability to access Home Assistant. Checking the console output is crucial; the presence of error messages like systemd-journald [115] failed to write entry xx items, xxx bytes), ignoring: Read-only file system strongly suggests that the file system has been remounted as read-only due to SCSI timeouts. Unfortunately, the system logs themselves may be inaccessible because they are stored on the read-only file system. However, if you have external logging mechanisms in place, such as sending logs to a remote server, these logs may provide valuable insights into the events leading up to the issue. Monitoring the Hypervisor's performance is also vital. High CPU utilization, memory pressure, or disk I/O bottlenecks on the Hypervisor can contribute to SCSI timeouts. Tools provided by the Hypervisor, such as performance charts and resource monitoring dashboards, can help identify these issues. Specifically, look for periods where the virtual machine's disk I/O latency is high, as this can indicate that SCSI commands are taking longer than expected to complete. By correlating system unresponsiveness with error messages and Hypervisor performance data, you can confidently diagnose SCSI timeout problems.

Examining Logs and System Information

When troubleshooting SCSI timeout issues, examining logs and system information can provide valuable clues. As mentioned earlier, the system logs within the virtual machine may be inaccessible if the file system is read-only. However, if you have implemented external logging, these logs should be the first place to look. Search for error messages related to SCSI timeouts or disk I/O errors. These messages can pinpoint the exact time when the issue occurred and may provide context about the operations that were being performed. In addition to logs, gathering system information is crucial. The System Information section provided in the initial issue description contains a wealth of details about the Home Assistant setup, including the operating system version, hardware details, and installed add-ons. This information can help identify potential compatibility issues or known problems with specific hardware configurations. For example, the Proxmox version (8.4.1) and the Home Assistant OS version (16.0) can be checked against known issues or compatibility reports. Details about the virtualization environment (KVM), board (OVA), and network configuration can also be relevant. Furthermore, the information about installed add-ons and their versions can help rule out conflicts or bugs in specific add-ons that might be contributing to the problem. By systematically reviewing these logs and system details, you can build a comprehensive understanding of the environment and identify potential causes of SCSI timeouts.

Solution: Increasing SCSI Timeout Values

The reported solution to this issue involves increasing the SCSI timeout values. The default timeout value of 30 seconds appears to be insufficient under high load conditions. By increasing this timeout, the system allows more time for SCSI commands to complete, reducing the likelihood of false positives that lead to the file system being remounted as read-only. The user in the initial issue description found that setting the timeout values to 300 seconds resolved the problem. This can be achieved by executing the following commands:

echo 300 > /sys/block/sda/device/timeout
echo 300 > /sys/block/sda/device/eh_timeout

These commands write the value 300 (representing 300 seconds) to the timeout and eh_timeout files for the sda device. The timeout parameter specifies the standard SCSI command timeout, while eh_timeout is related to the error handling timeout. Increasing both values ensures that the system has ample time to recover from transient issues. However, it is crucial to understand that this change is not persistent across reboots. After each reboot, these commands need to be executed again. This temporary nature highlights the need for a more permanent solution, which will be discussed in the next section. While increasing the timeout values is a relatively simple fix, it is essential to implement it correctly and consider its implications. A too-high timeout value can mask underlying issues, while an insufficient value may not resolve the problem effectively.

Making the Change Persistent

The primary drawback of the manual solution described above is that it is not persistent across reboots. To make the change permanent, you need to configure the system to apply these settings automatically during startup. There are several ways to achieve this, each with its own advantages and disadvantages. One common approach is to create a systemd service that runs these commands at boot time. Systemd is the system and service manager used by many Linux distributions, including Home Assistant OS. A systemd service is a unit configuration file that defines how a service should be managed, including when it should start, stop, and restart. Creating a service ensures that the timeout values are set each time the system boots. Another method is to use rc.local, a script that is traditionally executed late in the boot process. However, the use of rc.local is becoming less common, and systemd services are generally preferred. Regardless of the method chosen, it is essential to ensure that the script or service is correctly configured and enabled so that the timeout values are set reliably. Proper testing is also crucial to verify that the changes persist after a reboot. A persistent solution not only saves manual effort but also ensures that the system remains stable and protected against SCSI timeouts.

Implementing a Permanent Solution

To implement a permanent solution, creating a systemd service is a robust and recommended approach. Systemd services are managed by the systemd system and service manager, providing a reliable way to execute commands at boot time. Here’s how to create a systemd service to set the SCSI timeout values:

Create a script: First, create a script that contains the commands to set the timeout values. This script will be executed by the systemd service.
```
#!/bin/bash
echo 300 > /sys/block/sda/device/timeout
echo 300 > /sys/block/sda/device/eh_timeout
exit 0
```
Save this script to a location such as /usr/local/bin/set_scsi_timeout.sh. Make sure the script is executable by running chmod +x /usr/local/bin/set_scsi_timeout.sh.
Create a systemd service file: Next, create a systemd service file. This file defines the service and specifies how it should be managed.
```
[Unit]
Description=Set SCSI Timeout
After=local-fs.target

[Service]
Type=oneshot
ExecStart=/usr/local/bin/set_scsi_timeout.sh
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
```
Save this file as set-scsi-timeout.service in the /etc/systemd/system/ directory. Let's break down the key sections of this file:
- [Unit]: This section provides general information about the service.
  - Description: A human-readable description of the service.
  - After=local-fs.target: This directive ensures that the service starts after the local file systems are mounted, which is necessary for accessing the /sys/block/sda/device/ path.
- [Service]: This section defines the service execution parameters.
  - Type=oneshot: This specifies that the service executes a single command and then exits.
  - ExecStart: The command to execute, which is the path to the script we created earlier.
  - RemainAfterExit=yes: This ensures that the service is considered active even after the script has finished executing.
- [Install]: This section specifies how the service should be enabled and started.
  - WantedBy=multi-user.target: This indicates that the service should be started when the system enters the multi-user mode, which is the normal operating mode.
Enable and start the service:

After creating the service file, you need to enable and start the service using systemd commands:

sudo systemctl enable set-scsi-timeout.service sudo systemctl start set-scsi-timeout.service ```

The `enable` command creates the necessary symbolic links to ensure that the service starts at boot time. The `start` command starts the service immediately.

Verify the service:

To verify that the service is running correctly, you can check its status using:

sudo systemctl status set-scsi-timeout.service ```

This command will display information about the service, including whether it is active and any recent log messages. You can also check the timeout values after a reboot to ensure that they have been set correctly.

By following these steps, you can create a systemd service that persistently sets the SCSI timeout values, ensuring that your system remains stable even under high load conditions. This solution provides a reliable and automated way to mitigate SCSI timeout issues, reducing the risk of file system remounts and system unresponsiveness.

Additional Considerations and Best Practices

While increasing the SCSI timeout values can mitigate the immediate issue of file system remounts, it is crucial to consider other factors that might be contributing to the problem. Simply increasing the timeout may mask underlying issues such as hardware problems or resource contention within the Hypervisor. Therefore, a comprehensive approach to system stability involves not only adjusting timeout values but also monitoring system performance and addressing potential bottlenecks. Regularly monitoring the Hypervisor's resource utilization, including CPU, memory, and disk I/O, can help identify periods of high load that might trigger SCSI timeouts. If high load is a recurring issue, consider optimizing the virtual machine's resource allocation or upgrading the underlying hardware. Additionally, ensure that the storage subsystem is performing optimally. This might involve checking the health of the physical disks, optimizing the storage configuration, or considering the use of faster storage media. Keeping the operating system and Hypervisor software up to date is also essential, as updates often include performance improvements and bug fixes that can address SCSI-related issues. It’s also a good practice to implement proper logging and alerting mechanisms. Configuring the system to send logs to a remote server can ensure that you have access to diagnostic information even when the local file system is read-only. Setting up alerts for high resource utilization or SCSI errors can provide early warnings of potential problems, allowing you to take proactive measures before they escalate. By combining these best practices with the solution of increasing SCSI timeout values, you can create a more resilient and stable Home Assistant environment.

Conclusion

SCSI timeouts leading to read-only file system remounts can be a frustrating issue for Home Assistant users running virtualized environments. However, by understanding the root causes and implementing appropriate solutions, you can effectively mitigate this problem. This article has provided a comprehensive guide to diagnosing and resolving SCSI timeout issues, with a focus on increasing the timeout values and making the change persistent through a systemd service. While increasing timeout values is a practical solution, it is essential to consider the broader context of system performance and address any underlying issues that might be contributing to the problem. Regularly monitoring system resources, optimizing storage configurations, and implementing proper logging and alerting mechanisms are all critical components of a robust and stable Home Assistant setup. By following the steps outlined in this guide and adopting a proactive approach to system management, you can ensure that your Home Assistant environment remains reliable and responsive, even under high load conditions. Remember, a stable system is a foundation for a seamless smart home experience.