Unexpected error during recovery failing shard – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-2.9

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Briefly, this error occurs when OpenSearch encounters an unexpected issue during the recovery process of a shard, causing the shard to fail. This could be due to hardware issues, network problems, or data corruption. To resolve this, you can try relocating the shard to another node, checking the hardware for any issues, or restoring the shard from a backup. If the problem persists, you may need to reindex the data.

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This guide will help you check for common problems that cause the log ” unexpected error during recovery [{}]; failing shard ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: recovery, indices, shard.

Log Context

Log “unexpected error during recovery [{}]; failing shard” classname is PeerRecoveryTargetService.java.
We extracted the following from OpenSearch source code for those seeking an in-depth context :

        public void onFailure(Exception e) {
            try (ReplicationRef recoveryRef = onGoingRecoveries.get(recoveryId)) {
                if (recoveryRef != null) {
                    logger.error(() -> new ParameterizedMessage("unexpected error during recovery [{}]; failing shard"; recoveryId); e);
                        new RecoveryFailedException(recoveryRef.get().state(); "unexpected error"; e);
                        true // be safe


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