Before you begin reading this guide, we recommend you try running the Elasticsearch Error Check-Up which analyzes 2 JSON files to detect many configuration errors.
Briefly, this error occurs when Elasticsearch is unable to read the repository data from the index blob in the repository. This could be due to issues with the repository or issues with the data stored in the repository. You will need to resolve the issue to create a successful snapshot.
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This guide will help you check for common problems that cause the log ” could not read repository data from index blob ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: repositories, repository, blobstore and index.
Overview
An Elasticsearch snapshot provides a backup mechanism that takes the current state and data in the cluster and saves it to a repository (read snapshot for more information). The backup process requires a repository to be created first. The repository needs to be registered using the _snapshot endpoint, and multiple repositories can be created per cluster. The following repository types are supported:
Repository types
| Repository type | Configuration type |
|---|---|
| Shared file system | Type: “fs” |
| S3 | Type : “s3” |
| HDFS | Type :“hdfs” |
| Azure | Type: “azure” |
| Google Cloud Storage | Type : “gcs” |
Examples
To register an “fs” repository:
PUT _snapshot/my_repo_01
{
"type": "fs",
"settings": {
"location": "/mnt/my_repo_dir"
}
}Notes and good things to know
- S3, HDFS, Azure and Google Cloud require a relevant plugin to be installed before it can be used for a snapshot.
- The setting, path.repo: /mnt/my_repo_dir needs to be added to elasticsearch.yml on all the nodes if you are planning to use the repo type of file system. Otherwise, it will fail.
- When using remote repositories, the network bandwidth and repository storage throughput should be high enough to complete the snapshot operations normally, otherwise you will end up with partial snapshots.
Log Context
Log “could not read repository data from index blob”classname is BlobStoreRepository.java We extracted the following from Elasticsearch source code for those seeking an in-depth context :
// operations must start from the EMPTY_REPO_GEN again
if (latestKnownRepoGen.compareAndSet(indexGen; RepositoryData.EMPTY_REPO_GEN)) {
logger.warn("Resetting repository generation tracker because we failed to read generation [" + indexGen + "]"; ioe);
}
}
throw new RepositoryException(metadata.name(); "could not read repository data from index blob"; ioe);
}
}
private static String testBlobPrefix(String seed) {
return TESTS_FILE + seed;
Find & fix Elasticsearch problems
