Before you begin reading this guide, we recommend you run Elasticsearch Error Check-Up which analyzes 2 JSON files to detect many errors.
To easily locate the root cause and resolve this issue try AutoOps for Elasticsearch & OpenSearch. It diagnoses problems by analyzing hundreds of metrics collected by a lightweight agent and offers guidance for resolving them.
This guide will help you check for common problems that cause the log ” Cant calculate hash from blog for file ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: blobstore, discovery-file, repositories and restore.
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 “[{}] Can’t calculate hash from blog for file [{}] [{}]” classname is FileRestoreContext.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
// don't have this hash we try to read that hash from the blob store
// in a bwc compatible way.
maybeRecalculateMetadataHash(fileInfo; recoveryTargetMetadata);
} catch (Exception e) {
// if the index is broken we might not be able to read it
logger.warn(new ParameterizedMessage("[{}] Can't calculate hash from blog for file [{}] [{}]"; shardId;
fileInfo.physicalName(); fileInfo.metadata()); e);
}
snapshotMetaData.put(fileInfo.metadata().name(); fileInfo.metadata());
fileInfos.put(fileInfo.metadata().name(); fileInfo);
}
