Object Versioning

Setup Usage

Object Versioning preserves deleted objects as versioned, noncurrent objects that remain accessible in your bucket until explicitly removed. This feature is used to track changes to objects and to enable recovery of specific versions of an object. This page describes the feature and the options available when using it.

We recommend that you use soft delete instead of Object Versioning to protect against permanent data loss from accidental or malicious deletions. To learn more about when to use soft delete and Object Versioning, see Considerations.

Introduction

You enable Object Versioning for a bucket. Once enabled:

  • Cloud Storage retains a noncurrent object version each time you replace or delete a live object version, as long as you do not specify the generation number of the live version.

    • Noncurrent versions retain the name of the object, but are uniquely identified by their generation number.

    • Noncurrent versions only appear in requests that explicitly call for them to be included.

  • You delete a noncurrent version of an object by including the generation number in the deletion request or by using Object Lifecycle Management.

  • In a bucket with soft delete enabled, when you delete a noncurrent object, Cloud Storage changes its state to soft-deleted. A soft-deleted object is permanently deleted after its soft delete retention period expires.

  • Noncurrent versions of objects exist independently of any live version.

If you disable Object Versioning:

  • The bucket no longer accumulates new noncurrent versions of objects.

  • Object versions that already exist in the bucket are unaffected.

Considerations

  • There is no default limit on the number of object versions you can have. Each noncurrent version of an object is charged at the same rate it was when it was live.

  • Early deletion charges apply only when an object version is removed from the bucket, not when the version becomes noncurrent. The storage duration for a version removed from a bucket is based on the time it was added to the bucket, not the time it became noncurrent.

  • If you enable versioning, consider using Object Lifecycle Management, which can remove older versions of an object after a specified length of time or as newer versions become noncurrent. For one possible setup, see the lifecycle configuration example for deleting objects.

  • To determine whether to enable Object Versioning or soft delete on your bucket, consider the following points:

    • If you want to prevent permanent data loss from accidental or malicious deletions, use soft delete instead of Object Versioning. soft delete provides bucket-level protection by retaining all recently deleted live or noncurrent objects. It also can protect against bucket-level deletions.

    • If you have specific billing requirements and have configured Object Lifecycle Management rules to retain a specified number of noncurrent versions, use Object Versioning.

      In such a scenario, you only get partial protection from accidental deletions because Object Versioning does not protect against bucket-level events or undesired noncurrent object deletions.

    • Noncurrent objects are accessible and readable, while soft-deleted objects are retained offline and are non-readable. Restoring soft-deleted objects requires specific IAM permissions that are available to the Storage Admin (roles/storage.admin) IAM role.

      If you want access to the most recently deleted objects and a high level of protection against permanent data loss from accidental and malicious deletion events, you can enable Object Versioning and soft delete on the same bucket. You can configure the Object Lifecycle Management policy to automatically delete noncurrent versions after a specific number of days, and then use soft delete to provide an additional layer of protection.

Noncurrent object metadata

Noncurrent versions of objects have their own metadata, which may differ from the metadata of the live version. Most importantly, a noncurrent version retains its ACLs and does not necessarily have the same permissions as the live version.

Each version, whether live or noncurrent, has one set of metadata; only the latest metageneration number refers to metadata. Older metageneration numbers cannot be used to access metadata that has since been changed.

You can update metadata for a noncurrent version of an object by specifying its generation in your request. To ensure safe read-modify-write semantics, you can use a metageneration-match precondition. Using this precondition causes the update to fail if the metadata you are attempting to update was changed between the time you read the metadata and sent the update.

Object Versioning example

This example shows what happens to the file cat.jpg in a bucket with Object Versioning and soft delete enabled as you replace, update, and delete the file.

You upload a new image

When you first upload cat.jpg to Cloud Storage, it receives a generation number and a metageneration number. In this example, the generation number is 1360887697105000. Because the object is new, the metageneration number is 1.

cat.jpg receives generation and metageneration numbers even though Object Versioning is not enabled. You can obtain these numbers by viewing the object metadata.

You enable Object Versioning

At this point, you decide to enable Object Versioning for your bucket. Doing so does not affect the generation or metageneration numbers of cat.jpg.

You change the metadata of the image

You update the metadata for cat.jpg by adding custom metadata: color:black. Updating metadata causes the metageneration value of cat.jpg to increase, in this case from 1 to 2. However, the object itself remains unchanged, so Cloud Storage continues to store only one version of cat.jpg, and the version continues to have a generation number of 1360887697105000.

You upload a new version of the image

You upload a new version of cat.jpg to your Cloud Storage bucket. When you do so, Object Versioning moves the existing cat.jpg object into a noncurrent state. The noncurrent version retains the same storage class and metadata it previously had. The noncurrent version appears only if you perform a versioned listing: it does not appear in normal listing commands. The noncurrent version is now referenced as: cat.jpg#1360887697105000.

Meanwhile, the newly uploaded cat.jpg becomes the live version of the object. This new cat.jpg gets its own generation number, in this example 1360887759327000. It also gets its own metadata and a metageneration number of 1, which means it does not contain the color:black metadata unless you specify it. When you access or modify cat.jpg, this is the version that is used. You can alternatively refer to this version of cat.jpg using its generation number. For example, when using the Google Cloud CLI, you would refer to it as cat.jpg#1360887759327000.

You delete the live version of the image

You now delete cat.jpg. When you do this, the version that had generation number 1360887759327000 becomes noncurrent. Your bucket now contains two noncurrent versions of cat.jpg and no live versions. You can still refer to either noncurrent version by using its generation number, but if you try to access cat.jpg without a generation number, it fails.

Similarly, a normal object listing of the bucket will not show cat.jpg as one of the objects in the bucket. For information on listing noncurrent versions of objects, see Listing noncurrent object versions.

You disable Object Versioning

You disable Object Versioning, which stops objects from becoming noncurrent. Existing noncurrent versions of objects remain in Cloud Storage. Even though Object Versioning is disabled, cat.jpg#1360887697105000 and cat.jpg#1360887759327000 remain stored in your bucket until you delete them.

You restore one of the noncurrent versions

Even with Object Versioning disabled, you can make a copy of one of the existing noncurrent versions, which effectively restores the version. Once you do this, your bucket has three versions of cat.jpg: the two noncurrent versions and the live version that came from restoring.

You delete one of the noncurrent versions

You can delete a noncurrent version of an object manually or by using Object Lifecycle Management.

When you delete a noncurrent version, cat.jpg#1360887697105000, it gets soft-deleted. This soft-deleted object is retained for the soft delete retention duration specified in the soft delete policy of the bucket. After the retention duration expires, Cloud Storage permanently deletes the soft-deleted version of this object.

You restore one of the soft-deleted object versions

Even with Object Versioning disabled, you can restore a soft-deleted version of a noncurrent object. A copy of a soft-deleted version is restored as the live version with new object metadata and a new creation date. The original soft-deleted object also remains in the bucket and is permanently deleted after its soft delete retention duration expires.

Object Versioning reference

This reference table shows what happens when you take certain actions with Object Versioning.

Object Versioning status Soft delete status Action Result
Disabled Disabled
Delete dog.png. dog.png is permanently deleted.
Delete a noncurrent version of dog.png by specifying its generation number.1 The noncurrent version is permanently deleted.
Replace dog.png with a new version. The new version replaces the live version and receives a new generation number. The old live version is permanently deleted.
Copy a noncurrent version of dog.png over the live version.1 A copy of the noncurrent version replaces the live version and receives a new generation number. The old live version is permanently deleted.
Disabled Enabled
Delete dog.png. dog.png is soft-deleted.
Delete a noncurrent version of dog.png by specifying its generation number.1 The noncurrent version is soft-deleted.
Replace dog.png with a new version. The new version replaces the live version and receives a new generation number. The old live version is soft-deleted.
Copy a noncurrent version of dog.png over the live version.1 A copy of the noncurrent version replaces the live version and receives a new generation number. The old live version is soft-deleted.
Enabled Disabled
Delete the live version of dog.png without specifying its generation number. The live version becomes a noncurrent version and keeps the same generation number.
Delete the live version of dog.png by specifying its generation number. The live version is permanently deleted.
Delete a noncurrent version of dog.png by specifying its generation number. The noncurrent version is permanently deleted.
Replace dog.png with a new version. The new version replaces the live version and receives a new generation number. The old live version becomes a noncurrent version and keeps the same generation number.
Copy a noncurrent version of dog.png over the live version. A copy of the noncurrent version replaces the live version and receives a new generation number. The old live version becomes a noncurrent version and keeps the same generation number.
Enabled Enabled
Delete the live version of dog.png without specifying its generation number. The live version becomes a noncurrent version and keeps the same generation number.
Delete the live version of dog.png by specifying its generation number. The live version is soft-deleted.
Delete a noncurrent version of dog.png by specifying its generation number. The noncurrent version is soft-deleted.
Replace dog.png with a new version. The new version replaces the live version and receives a new generation number. The old live version becomes a noncurrent version and keeps the same generation number.
Copy a noncurrent version of dog.png over the live version. A copy of the noncurrent version replaces the live version and receives a new generation number. The old live version becomes a noncurrent version and keeps the same generation number.

1 A noncurrent version might exist if the bucket had Object Versioning enabled previously.

File restoration behavior

You can effectively restore a noncurrent object version to the current live version. See Restoring noncurrent object versions for a step-by-step guide to doing so.

When you do this with Object Versioning enabled, if there already exists a live version of the object in your bucket, Cloud Storage replaces the existing live version but also retains it as a new noncurrent version. In such a case, your bucket subsequently contains the replaced object (now noncurrent) and two copies of the object that was previously noncurrent (one live copy and one still-noncurrent copy), all of which incur storage charges. To prevent unnecessary charges, delete the noncurrent version that you used to make the current live copy, or configure Object Lifecycle Management to remove noncurrent objects when they meet the conditions you specify.

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