Briefly, this error occurs when Elasticsearch is unable to compute the hash value for a blob file. This could be due to issues with the file itself, such as corruption, or problems with the file’s permissions. To resolve this issue, you can try re-uploading the file, checking the file for corruption, or verifying that Elasticsearch has the necessary permissions to access the file. If the problem persists, consider checking the Elasticsearch logs for more detailed error information.
This guide will help you check for common problems that cause the log ” {} Can’t calculate hash from blob for file [{}] [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: repositories, 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 “{} Can’t calculate hash from blob for file [{}] [{}]” classname is BlobStoreRepository.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
// to ensure we don't double the space in the repo since old snapshots
// don't have this hash we try to read that hash from the blob store
// in a bwc compatible way.
maybeRecalculateMetadataHash(blobContainer; fileInfo; metadata);
} catch (Exception e) {
logger.warn(() -> new ParameterizedMessage("{} Can't calculate hash from blob for file [{}] [{}]";
shardId; fileInfo.physicalName(); fileInfo.metadata()); e);
}
if (fileInfo.isSame(md) && snapshotFileExistsInBlobs(fileInfo; blobs)) {
// a commit point file with the same name; size and checksum was already copied to repository
// we will reuse it for this snapshot
