As opposed to a full backup which uploads a complete copy of each file to a storage, a block-level backup uploads the full copy of your data only during the first execution of the backup plan and when explicitly forced to do this. In other cases, the backup service uploads only blocks (parts of a file) that were modified since the last backup date, which can dramatically decrease the processing time required for completing your backup routine, as well as reduce the required storage space. However, unlike incremental backup, a block-level backup only uploads modified portions of files instead of uploading a full copy of each file that has been modified since the last backup was made.
The backup service decides whether a file needs to be updated based on its modification date. If a file was modified after it has been uploaded to a backup storage, the backup service breaks this file into blocks and then checks whether the hash string at the beginning of each block is different from that of the latest full version of this file stored in a backup. On finding any mismatch in block hashes, the corresponding portion of a file is uploaded to the storage.
The block size varies for different kind of backup data. When using a block-level file backup, the block size depends on the file size:
- The block size equals 128 kB if a file size is less than 512 GB.
- The block size equals 256 kB if a file size is less than 1024 GB.
- The block size equals 512 kB if a file size exceeds 1024 GB.
When performing a block-level backup, you can schedule a full backup as well, to be able to purge outdated file versions according to the current retention policy settings. The backup service cannot delete a previous file version unless a newer full backup is uploaded to the storage, because this version is used for restoring the file.
You can manually force a full backup at any time by clicking the corresponding command under the backup plan entry on the Backup Plans tab of your application.
CloudBerry Backup uses different approaches for processing various kinds of backups. For this reason, block-level backup may become unavailable when using certain storage providers as a destination for your backups. See Feature Comparison by Storage Providers for more information.