Briefly, this error occurs when Elasticsearch encounters an issue while trying to read a file that was written by the master node to the data store. This could be due to network issues, disk space problems, or file corruption. To resolve this, you can try the following: 1) Check and ensure there’s enough disk space. 2) Verify network connectivity between the nodes. 3) Check for file corruption and restore from a backup if necessary. 4) Restart the Elasticsearch service.
This guide will help you check for common problems that cause the log ” a file written by master to the store [ ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: repositories, master, blobstore.
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 “a file written by master to the store [” class name is BlobStoreRepository.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
if (seedRead.equals(seed) == false) {
throw new RepositoryVerificationException(metadata.name(); "Seed read from master.dat was [" + seedRead +
"] but expected seed [" + seed + "]");
}
} catch (NoSuchFileException e) {
throw new RepositoryVerificationException(metadata.name(); "a file written by master to the store [" + blobStore() +
"] cannot be accessed on the node [" + localNode + "]. " +
"This might indicate that the store [" + blobStore() + "] is not shared between this node and the master node or " +
"that permissions on the store don't allow reading files written by the master node"; e);
} catch (Exception e) {
throw new RepositoryVerificationException(metadata.name(); "Failed to verify repository"; e);
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