Elasticsearch IndexShardSnapshotFailedException: Index shard snapshot failed - Common Causes & Fixes

Brief Explanation

The "IndexShardSnapshotFailedException: Index shard snapshot failed" error occurs in Elasticsearch when there's a problem creating a snapshot of a specific index shard. This error indicates that the snapshot process for one or more shards within an index has failed.

Impact

This error can have significant impact on your Elasticsearch cluster:

• Incomplete backups: Failed shard snapshots result in incomplete backups, potentially leading to data loss or recovery issues.
• Increased storage usage: Failed snapshots may leave behind partial data, consuming unnecessary storage space.
• Reduced cluster performance: Repeated snapshot attempts can strain cluster resources.

Common Causes

1. Insufficient disk space in the snapshot repository
2. Network issues during snapshot creation
3. Corrupted index or shard data
4. Concurrent index operations during snapshot creation
5. Elasticsearch version incompatibilities
6. Insufficient permissions for the Elasticsearch process

Troubleshooting and Resolution Steps

1. Check available disk space:

   • Ensure there's sufficient space in the snapshot repository.
   • Clean up old or unnecessary snapshots.

2. Verify network connectivity:

   • Check network stability between Elasticsearch nodes and the snapshot repository.
   • Ensure firewall rules allow necessary traffic.

3. Examine Elasticsearch logs:

   • Look for specific error messages related to the failed snapshot.
   • Check for any concurrent operations that might interfere with the snapshot process.

4. Verify index health:

   • Use the _cat/indices API to check the status of the affected index.
   • Consider running a _forcemerge on the index before retrying the snapshot.

5. Check Elasticsearch versions:

   • Ensure all nodes in the cluster are running the same Elasticsearch version.
   • Verify compatibility between the snapshot repository and Elasticsearch version.

6. Review permissions:

   • Check that the Elasticsearch process has the necessary permissions to write to the snapshot repository.

7. Retry the snapshot:

   • If the issue persists, try taking a snapshot of individual indices rather than the entire cluster.

8. Consider restoring from a previous snapshot:

   • If the index is corrupted, restore from a known good snapshot and retry.

Best Practices

• Regularly monitor available disk space in snapshot repositories.
• Implement automated cleanup of old snapshots to manage storage efficiently.
• Schedule snapshots during periods of low cluster activity.
• Use the wait_for_completion=false parameter for large snapshots to avoid timeouts.
• Implement a monitoring system to alert on failed snapshots.

Frequently Asked Questions

Q: Can I take a snapshot of a single shard instead of the entire index?
A: Elasticsearch doesn't support snapshots of individual shards. Snapshots are taken at the index level or for multiple indices.

Q: How can I identify which specific shard failed during the snapshot process?
A: Check the Elasticsearch logs for detailed error messages. You can also use the _cat/shards API to identify any problematic shards in the index.

Q: Will a failed shard snapshot affect other successful shard snapshots in the same operation?
A: No, Elasticsearch snapshots are incremental. Successful shard snapshots will be retained even if other shards fail.

Q: Can I resume a failed snapshot operation?
A: Elasticsearch doesn't support resuming failed snapshots. You'll need to start a new snapshot operation.

Q: How can I prevent this error from occurring in the future?
A: Implement regular health checks, ensure adequate storage, schedule snapshots during low-traffic periods, and keep your Elasticsearch cluster updated to minimize the risk of snapshot failures.