File Backups in Immutable Repositories

For general information on the immutability feature for object storage repositories in Veeam Backup & Replication and on how to configure it, see the Immutability for Object Storage Repositories section.

How Immutability for NAS Backup Works

Immutability settings configured for a repository where you store a file share are applied to the whole backup of the file share, that is to all backup files protecting the file share. Thus, the immutability configured for the repository starts its countdown for the backup files when Veeam Backup & Replication marks some old file versions and their data blocks for deletion according to the retention settings configured in the backup job. Files are deleted from the backup repository when the immutability lock is released for them. The period of the immutability lock is defined by the immutability settings of the backup repository and the block generation period, which is 10 days. For an example of how this mechanism works, see Case 8 in the File Backup Retention Scenarios section.


We strongly recommend the following configuration for storing NAS backups in immutable object storage repositories:

  • Set the retention period for the immutable object storage repository to 14 days.
  • Configure NAS backup jobs that use the immutable object storage repository to run not more than once per day.

Otherwise, NAS backup may consume too much storage space.

These settings are critical for cloud object storage repositories where the cost of the disk space consumed for storing file versions may be very high.


You can quickly roll back a file share backup stored on an immutable short-term repository to a point in time state by using the Sync-VBRNASBackupState PowerShell cmdlet.

Block Generation

Apart from the immutability period set for the object storage repository, Veeam Backup & Replication automatically adds 10 days to the immutability expiration date to reduce I/O operations and associated costs. This period is called Block Generation. You do not have to configure it, the Block Generation setting is applied automatically. For example, if you set your immutability period to 14 days for your object storage repository, Veeam Backup & Replication adds 10 days to specific objects to reduce I/O operations with the data blocks over time. Thus, you will have immutability set for 14 days + 10 days of Block Generation set for data blocks in your object storage repositories, so the actual immutability period will equal to 24 days. For more information, see Block Generation for object storage repositories.

Metadata of File Backups in Immutable Object Storage Repositories (Cloud, S3-Compatible)

When creating file backups in the backup repository, Veeam Backup & Replication creates metadata in the same repository next to the data. Data in immutable repositories is temporarily locked and cannot be changed or removed. When file backups are stored in the immutable repository, the copy of metadata that is stored next to the data is also immutable and cannot be changed till the immutability period ends. The immutability period is applied to all the files referring to the file backup.

The examples below show the cases when the immutability period is set to 20 days, plus a 10-day lock for block generation. Thus, all locked metadata and data files can be changed or removed only after day 30.

To solve the problem of locked metadata, Veeam Backup & Replication creates two sets of metadata: locked metadata, which is stored next to the data and cannot be changed or removed till the immutability period is over, and active meta data, which changes actively during every backup session and keeps the up-to-date state of the file backup.

Depending on the type of the immutable repository, active metadata is stored on different infrastructure components.

Once a month or as the metadata chain reaches 30 generations, Veeam Backup & Replication uses metadata copy files created during this period to create a new locked metadata flat file. The schemas below show examples of creating a locked metadata flat file for a job that runs once every day.

After the immutability period for the metadata copy files, which were already transformed into the metadata flat file, ends, Veeam Backup & Replication removes them from the object storage repository.

Metadata in Immutable Cloud Object Storage Repositories

If file backups are stored in an immutable cloud object storage such as Amazon S3, Microsoft Azure Storage, IBM Cloud Object Storage, Wasabi Cloud Object Storage, or S3-compatible object storage, the active metadata is stored on the cache repository.

File Backups in Immutable Repositories 

Metadata in Hardened Repositories and Immutable Deduplicating Storage Appliances

If file backups are stored in an immutable hardened repository or HPE StoreOnce deduplicating storage appliance, the active metadata is stored on the immutable repository alongside with the locked metadata copy and locked backup data.

File Backups in Immutable Repositories