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HeadObject

Contributors netapp-lhalbert netapp-madkat
PDFs

You can use the S3 HeadObject request to retrieve metadata from an object without returning the object itself. If the object is stored in a Cloud Storage Pool, you can use HeadObject to determine the object's transition state.

HeadObject and multipart objects

You can use the partNumber request parameter to retrieve metadata for a specific part of a multipart or segmented object. The x-amz-mp-parts-count response element indicates how many parts the object has.

You can set partNumber to 1 for both segmented/multipart objects and non-segmented/non-multipart objects; however, the x-amz-mp-parts-count response element is only returned for segmented or multipart objects.

UTF-8 characters in user metadata

StorageGRID does not parse or interpret escaped UTF-8 characters in user-defined metadata. HEAD requests for an object with escaped UTF-8 characters in user-defined metadata don't return the x-amz-missing-meta header if the key name or value includes unprintable characters.

Unsupported request header

The following request header is not supported and returns XNotImplemented:

  • x-amz-website-redirect-location

Versioning

If a versionId subresource is not specified, the operation fetches the most recent version of the object in a versioned bucket. If the current version of the object is a delete marker, a "Not Found" status is returned with the x-amz-delete-marker response header set to true.

Request headers for server-side encryption with customer-provided encryption keys (SSE-C)

Use all three of these headers if the object is encrypted with a unique key that you provided.

  • x-amz-server-side-encryption-customer-algorithm: Specify AES256.

  • x-amz-server-side-encryption-customer-key: Specify your encryption key for the object.

  • x-amz-server-side-encryption-customer-key-MD5: Specify the MD5 digest of the object's encryption key.

Caution The encryption keys you provide are never stored. If you lose an encryption key, you lose the corresponding object. Before using customer-provided keys to secure object data, review the considerations in Use server-side encryption.

HeadObject responses for Cloud Storage Pool objects

If the object is stored in a Cloud Storage Pool, the following response headers are returned:

  • x-amz-storage-class: GLACIER

  • x-amz-restore

The response headers provide information about the state of an object as it is moved to a Cloud Storage Pool, optionally transitioned to a non-retrievable state, and restored.

State of object Response to HeadObject

Object ingested into StorageGRID but not yet evaluated by ILM, or object stored in a traditional storage pool or using erasure coding

200 OK (No special response header is returned.)

Object in Cloud Storage Pool but not yet transitioned to a non-retrievable state

200 OK

x-amz-storage-class: GLACIER

`x-amz-restore: ongoing-request="false", expiry-date="Sat, 23 July 20 2030 00:00:00 GMT"

Until the object is transitioned to a non-retrievable state, the value for expiry-date is set to some distant time in the future. The exact time of transition is not controlled by the StorageGRID system.

Object has transitioned to non-retrievable state, but at least one copy also exists on the grid

200 OK

x-amz-storage-class: GLACIER

`x-amz-restore: ongoing-request="false", expiry-date="Sat, 23 July 20 2030 00:00:00 GMT"

The value for expiry-date is set to some distant time in the future.

Note: If the copy on the grid is not available (for example, a Storage Node is down), you must issue a RestoreObject request to restore the copy from the Cloud Storage Pool before you can successfully retrieve the object.

Object transitioned to a non-retrievable state, and no copy exists on the grid

200 OK

x-amz-storage-class: GLACIER

Object in process of being restored from a non-retrievable state

200 OK

x-amz-storage-class: GLACIER

`x-amz-restore: ongoing-request="true"

Object fully restored to the Cloud Storage Pool

200 OK

x-amz-storage-class: GLACIER

`x-amz-restore: ongoing-request="false", expiry-date="Sat, 23 July 20 2018 00:00:00 GMT"

The expiry-date indicates when the object in the Cloud Storage Pool will be returned to a non-retrievable state.

Multipart or segmented objects in Cloud Storage Pool

If you uploaded a multipart object or if StorageGRID split a large object into segments, StorageGRID determines whether the object is available in the Cloud Storage Pool by sampling a subset of the object's parts or segments. In some cases, a HeadObject request might incorrectly return `x-amz-restore: ongoing-request="false" when some parts of the object have already been transitioned to a non-retrievable state or when some parts of the object have not yet been restored.

HeadObject and cross-grid replication

If you are using grid federation and cross-grid replication is enabled for a bucket, the S3 client can verify an object's replication status by issuing a HeadObject request. The response includes the StorageGRID-specific x-ntap-sg-cgr-replication-status response header, which will have one of the following values:

Grid Replication status

Source

  • SUCCESS: The replication was successful.

  • PENDING: The object hasn't been replicated yet.

  • FAILURE: The replication failed with a permanent failure. A user must resolve the error.

Destination

REPLICA: The object was replicated from the source grid.
Note StorageGRID does not support the x-amz-replication-status header.