Failed to start shard – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 1.3-1.3

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Briefly, this error occurs when Elasticsearch is unable to initialize a shard. This could be due to a variety of reasons such as insufficient disk space, corruption of shard data, or a configuration issue. To resolve this, you can try freeing up disk space, restoring the shard from a backup, or checking the shard’s configuration for any inconsistencies. If the shard data is corrupted, you may need to delete and recreate the shard. Always ensure to have a backup of your data to prevent data loss.

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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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