Addressing SSTable Corruption and Data Migration Challenges in Cassandra Environments

Problem:

The client is encountering a “SSTable corruption” issue when starting Cassandra in a new PLAB environment created using a CloudFormation template. After copying EBS volumes from a disaster recovery (DR) environment and making necessary adjustments in the cassandra.yaml file, they receive a series of NullPointerExceptions related to the SSTableReader while attempting to open SSTables. The logs also indicate a “Too many open files” error and mention corrupted SSTables in the data directory, leading to a forced exit of the Cassandra daemon. The client seeks assistance to resolve this issue and is open to discussing it in a call.

Process:

The troubleshooting and resolution process began with a detailed exchange between the client and the expert regarding data corruption and transfer issues in a Cassandra setup. Initially, the client faced challenges while attempting to copy Cassandra data by mounting EBS volumes from the DR environment to a lab environment. This approach failed due to metadata mismatches, such as IP addresses and hostnames, causing SSTable corruption.

Solution:

1. Adding a New Data Center (DC3): Replicating data across a new data center would ensure a fast and documented solution, but changes made in DC3 would affect other environments.
2. Exporting Data to CSV: This method allowed the creation of an independent environment where data could be modified freely without affecting production. However, this approach was more complex and time-consuming, potentially resulting in Cassandra timeouts.
3. Client Attempts and Feedback: The client had tried exporting and importing data previously but failed, prompting them to propose using EBS volumes instead. They wanted to mount EBS volumes, copy SSTables, Cassandra configuration files, and system metadata, expecting this to ensure the same configuration in the new environment.
4. Expert’s Analysis: The expert explained that Cassandra data contains node-specific metadata that can’t be ported this way. Moving EBS volumes results in invalid SSTables because of metadata conflicts, including IP address changes during EC2 instance provisioning.
5. Final Steps: The client proposed copying snapshots of the Cassandra nodes and restoring them on the new cluster. The expert warned that this might still trigger errors if Cassandra detects foreign metadata and recommended deleting or adjusting the data files before Cassandra reads them.
6. Final Steps: The client proposed copying snapshots of the Cassandra nodes and restoring them on the new cluster. The expert warned that this might still trigger errors if Cassandra detects foreign metadata and recommended deleting or adjusting the data files before Cassandra reads them.

Conclusion:

Throughout this process, the expert provided technical guidance and resources, including official Cassandra documentation, to help the client understand the limitations of certain approaches. Logs were requested to further analyze node failures, and the client was advised on how to restore Cassandra nodes that encountered memory issues during repairs.

The case highlighted the challenges of copying Cassandra data due to metadata dependencies. While the client proposed copying EBS volumes, the expert recommended either replicating data via a new data center or exporting/importing using CSV files. These solutions provided a more reliable approach, ensuring data integrity. As we received no further updates from the client, the case was closed, likely indicating that the issue was successfully resolved.