Troubleshooting 'Malformed JSON String' In Proxmox With TrueNAS

by Alex Johnson 64 views

Introduction: The ZFS over iSCSI Challenge

Hello everyone! I recently stumbled upon this repo and wanted to share my experiences. I've been using TrueNAS Scale for a couple of months, mainly relying on NFS for my storage needs. Recently, I decided to explore the possibilities of ZFS over iSCSI, hoping to optimize my setup. The transition hasn't been entirely smooth, and I encountered a few hurdles along the way. Specifically, I've been wrestling with a "malformed JSON string" error within the Proxmox GUI when trying to view my storage configurations. This article aims to break down the issue, share my setup, and offer potential solutions or insights for others facing the same problem.

My current setup involves Proxmox v9.0.11 (fully updated) and TrueNAS Scale v25.10.0 (also up-to-date). Getting the iSCSI connection to work required some trial and error. Eventually, I got things connected. However, when trying to view storage within the Proxmox GUI, the dreaded error message appeared. It's a bit cryptic, but essentially, Proxmox is having trouble interpreting the data it's receiving from TrueNAS. Let's delve into the details and see how we can fix it.

Understanding the 'Malformed JSON String' Error

The core of the problem lies in Proxmox's inability to correctly parse the JSON data it's getting from TrueNAS. JSON (JavaScript Object Notation) is a standard format for transmitting data on the web. It's human-readable and designed to be easily interpreted by machines. The error message is "malformed JSON string, neither tag, array, object, number, string or atom, at character offset 0". This means the data Proxmox is receiving isn't valid JSON. It's as if the data stream is starting with something that's not a valid JSON element. This can be caused by a variety of issues, ranging from network problems to configuration errors on either the Proxmox or TrueNAS side.

The error goes on to point to JSON::RPC::Common::Marshal::Text, which suggests the problem is within the JSON parsing process. This parsing failure prevents Proxmox from correctly displaying the storage details, making it difficult to manage your storage volumes through the GUI. This error can manifest in various ways, such as a blank storage list, incorrect storage sizes, or the complete inability to add or modify storage configurations.

Let's break down the potential causes and how to address them.

Examining the Configuration: A Closer Look

Here’s a snapshot of my configuration, which I believe is causing the error. This is what I have set up in the Proxmox storage configuration:

truenas: truenas-zfs-iscsi
        blocksize 16k
        pool default/zfs-over-iscsi
        isciprovider truenas
        portal 10.83.20.10
        target iqn.2005-10.org.freenas.ctl:proxmox
        shared 1
        sparse 1
        nowritecache 0
        truenas_apikey [REDACTED]
        truenas_apiv4_host 10.83.20.10
        truenas_use_ssl 1
        zfs-base-path /dev/zvol
        content images

I’ve included a few additional lines in the configuration to get it working, which I found in other discussions. These are:

        isciprovider truenas
        nowritecache 0
        zfs-base-path /dev/zvol
        content images

Looking at this configuration, we can identify several key points that influence the connection between Proxmox and TrueNAS via iSCSI. The isciprovider truenas line specifies the iSCSI provider to use. Then, portal and target settings define the IP address of the TrueNAS system and the iSCSI target name, respectively. The truenas_apikey is used for authentication. The zfs-base-path /dev/zvol tells Proxmox where to find the ZFS volumes on the TrueNAS server. The content images setting tells Proxmox that this storage is for images and templates. The other settings relate to performance and storage behaviour. Misconfigurations in any of these parameters can cause issues with the data transfer and potentially the JSON parsing.

Potential Causes and Troubleshooting Steps

Let's go through some common causes and solutions for the "malformed JSON string" error when integrating TrueNAS with Proxmox:

  1. Network Connectivity Issues: This is a primary suspect. The error might occur if Proxmox can't reliably communicate with the TrueNAS server. Make sure that there's proper network connectivity between the Proxmox host and the TrueNAS system. Check the network settings for both systems and ensure there are no firewalls blocking traffic on the iSCSI ports (typically port 3260) or any other ports used for the API communication. Try pinging the TrueNAS server from the Proxmox host to test basic connectivity. Also, check for any network congestion or latency issues that might be disrupting the data flow.

  2. iSCSI Configuration: Double-check your iSCSI settings on both TrueNAS and Proxmox. Ensure the target and initiator (Proxmox) are correctly configured. The iSCSI target should be accessible from the Proxmox server, and the initiator should be logged into the target. Verify that the IQN (iSCSI Qualified Name) is correct on both sides. In TrueNAS, check that the iSCSI target is enabled and the related LUNs are created and correctly mapped to the initiator.

  3. TrueNAS API and API Key: Problems with the TrueNAS API calls can lead to malformed JSON responses. Make sure the API key in your Proxmox configuration is correct and has the necessary permissions to access storage information on TrueNAS. Verify that the TrueNAS API is working correctly by testing it directly, or through tools like curl or Postman. Incorrect API key settings or disabled API access on TrueNAS are frequent causes of this error. Additionally, confirm that the TrueNAS API host and port are correctly defined in your Proxmox configuration. In the provided config, ensure that the truenas_apiv4_host is correct and reachable.

  4. SSL Certificate Issues: If you're using SSL (indicated by truenas_use_ssl 1), ensure the SSL certificate is valid and trusted by Proxmox. Certificate validation errors can prevent proper communication and cause the malformed JSON issue. You may need to import the TrueNAS SSL certificate into the Proxmox host's trusted certificate store. Incorrect or expired certificates may disrupt the data transmission process, leading to the error. Make sure your Proxmox server trusts the SSL certificate presented by your TrueNAS server. Check that the certificate is valid and matches the TrueNAS hostname.

  5. Proxmox Configuration Errors: Review the Proxmox storage configuration file (/etc/pve/storage.cfg) for any syntax errors or misconfigurations. The file can become corrupted or improperly edited, which might lead to the issue. Double-check your configuration to make sure it matches the settings recommended for ZFS over iSCSI and TrueNAS. Also, verify that the zfs-base-path is correctly set, as this is critical for Proxmox to locate your ZFS volumes. Ensure all the parameters are correctly defined, with no typos or missing information.

  6. TrueNAS Version Compatibility: Ensure that your TrueNAS version is compatible with the version of Proxmox you are running. Although you've mentioned both are up to date, there might be incompatibilities. Review the release notes of both Proxmox and TrueNAS to check for any known issues when using iSCSI. Sometimes, updates introduce changes that break integrations. Consider downgrading or upgrading to more stable versions.

  7. Firewall Rules: Ensure that firewalls on both Proxmox and TrueNAS are correctly configured to allow traffic between the two systems on the necessary ports, including the iSCSI port (usually 3260) and any ports used for API communication. Incorrectly configured firewall rules can block communication, causing data transfer failures and JSON parsing errors.

  8. ZFS and LUN Configuration on TrueNAS: Make sure the ZFS pool and the corresponding iSCSI LUNs are correctly configured on the TrueNAS side. Verify that the LUNs are properly mapped to the initiator (Proxmox), and that the ZFS pool is healthy and accessible. The underlying ZFS configuration can impact the data transfer. A misconfigured ZFS setup can lead to data integrity issues or retrieval problems, thereby leading to JSON parsing errors.

  9. Debugging Tools: Use debugging tools like tcpdump or Wireshark to capture network traffic between Proxmox and TrueNAS. Inspect the captured data to see what data is being transmitted. Look for any errors or anomalies in the iSCSI traffic or the API calls. You can analyze the captured network traffic to see whether the data from TrueNAS is well-formed or the source of the malformed JSON. This approach helps in identifying where the data transfer goes wrong.

  10. Restart Services: After making changes to the iSCSI configuration or the storage settings, restart the relevant services on both Proxmox and TrueNAS to ensure the changes are applied. You might also want to try restarting the Proxmox host to clear any cached data.

Advanced Troubleshooting: A Deeper Dive

If the basic checks don't work, consider these advanced steps:

  • Enable Debug Logging: Enable debug logging on both Proxmox and TrueNAS, if possible. This can provide more detailed information about the errors that are occurring. Look for specific error messages that might give you more clues. This is particularly useful for API-related issues.
  • Test with curl: Use the curl command to directly test API calls to TrueNAS from the Proxmox host. This can help you determine if the API is working correctly. This bypasses the Proxmox GUI and allows you to isolate whether the issue is with the API calls themselves.
  • Check Resource Availability: Monitor the CPU, memory, and disk I/O of both the Proxmox host and the TrueNAS server. Overloaded resources can cause communication problems. Make sure that both systems have sufficient resources to handle the iSCSI traffic. High CPU utilization, memory pressure, or slow disk I/O can contribute to the issues.
  • Review Proxmox Logs: Examine the Proxmox logs (/var/log/syslog and /var/log/pveproxy/access.log) for any specific error messages related to the TrueNAS storage. These logs can often provide more specific information about the issue. In particular, look for errors related to iSCSI, ZFS, or API calls.

Conclusion: Persistence and Problem Solving

Dealing with the "malformed JSON string" error can be frustrating, but don't give up! By carefully examining your configuration, checking network connectivity, and systematically troubleshooting each potential cause, you can often identify the root of the problem and get your ZFS over iSCSI setup working smoothly. Remember to check all the settings thoroughly, double-check your networking, and ensure that your API keys are correct. Also, if you’re using SSL, verify that your certificates are properly configured and trusted by the Proxmox server. Patience and a methodical approach are key. Happy troubleshooting, and hopefully, you'll be able to resolve this issue and enjoy the benefits of ZFS over iSCSI with TrueNAS on your Proxmox setup!

External Links:

For more in-depth information on iSCSI, I recommend checking out the documentation provided by FreeNAS. This resource can provide additional guidance and support, and help ensure the success of your storage solution.