Failed to start shard – How to solve related issues

Opster Team

Feb-20, Version: 1.7-8.0

Before you begin reading this guide, we recommend you run Elasticsearch Error Check-Up which analyzes 2 JSON files to detect many errors.

Briefly, this error occurs when Elasticsearch is unable to start a shard, which is a smaller part of an index that is distributed across multiple nodes. If a shard fails to start, it can cause data loss or inconsistency in the index. To resolve this issue, one can try checking the log files for more information on the specific error, making sure that the shard is not corrupted, or even allocating a new shard to the affected node.

To easily locate the root cause and resolve this issue try AutoOps for Elasticsearch & OpenSearch. It diagnoses problems by analyzing hundreds of metrics collected by a lightweight agent and offers guidance for resolving them. Take a self-guided product tour to see for yourself (no registration required).

This guide will help you check for common problems that cause the log ” Failed to start shard ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: cluster, indices and shard.

Log Context

Log “[{}][{}] failed to start shard” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

             handleRecoveryFailure(indexService; indexMetaData; shardRouting; sendShardFailure; e);

    private void handleRecoveryFailure(IndexService indexService; IndexMetaData indexMetaData; ShardRouting shardRouting; boolean sendShardFailure; Throwable failure) {
        logger.warn("[{}][{}] failed to start shard"; failure; indexService.index().name(); shardRouting.shardId().id());
        synchronized (mutex) {
            if (indexService.hasShard(shardRouting.shardId().id())) {
                try {
                    indexService.removeShard(shardRouting.shardId().id(); "recovery failure [" + ExceptionsHelper.detailedMessage(failure) + "]");
                } catch (IndexShardMissingException e) {


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