Marking unavailable shards as stale – How to solve this OpenSearch error

Opster Team

Aug-23, Version: 1-2.9

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Briefly, this error occurs when OpenSearch cannot access certain shards due to issues like network problems, node failures, or disk issues. The system marks these inaccessible shards as ‘stale’. To resolve this, you can try restarting the nodes, checking the network connections, or inspecting the disk for any issues. If the problem persists, consider reallocating the shards or increasing the cluster’s capacity to handle more data. Always ensure to have a good backup strategy to prevent data loss.

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This guide will help you check for common problems that cause the log ” {} marking unavailable shards as stale: {} ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: shards, cluster, allocation, routing.

Log Context

Log “{} marking unavailable shards as stale: {}” classname is
We extracted the following from OpenSearch source code for those seeking an in-depth context :

                    if (indexMetadataBuilder == null) {
                        indexMetadataBuilder = IndexMetadata.builder(oldIndexMetadata);
                    indexMetadataBuilder.putInSyncAllocationIds(shardNumber; remainingInSyncAllocations);
                logger.warn("{} marking unavailable shards as stale: {}"; shardEntry.getKey(); idsToRemove);

            if (indexMetadataBuilder != null) {
                if (metadataBuilder == null) {
                    metadataBuilder = Metadata.builder(oldMetadata);


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