Veeam BitLooker – “Deleted” does not necessarily mean actually deleted

A great new addition to Veeam Backup & Replication v9 is BitLooker (patent pending), this new feature is designed to cut down backup file size and replication bandwidth utilisation by 20% or more. Essentially it removes chunks of data congesting your backup storage and network resources with the below three capabilities

  • Excluding swap and hibernation files blocks
  • Excluding deleted files blocks
  • Excluding user-specified files and folders

Since NTFS never reclaims deleted data blocks* in the file system when files are deleted, this means that an image-based backup for a VM may have to process more data blocks than what are actually used in the file system

BitLooker works by analysing the NTFS Master File Table on the VM guest OS to identify deleted file blocks and zeros out these blocks. If a data block of the VM image contains only the deleted file blocks, Veeam Backup & Replication does not read this data block from the source volume.
If a data block of the VM image contains zeroed out blocks and other data, Veeam Backup & Replication copies this block to the target

 

Veeam_BitLooker

 

By doing so, it reduces the size of an image-level backup file and bandwidth consumption for replication jobs.

Things to remember

  • Veeam Backup & Replication can only exclude deleted file blocks on the VM guest OS with Microsoft NTFS.
  • File exclusions can only be performed on a running VM
  • For users upgrading from previous versions: By default, BitLooker will be enabled for newly created jobs upon upgrade. However, it will not be automatically enabled on existing jobs to ensure the jobs do not change existing behaviors. BitLooker can be enabled manually in the advanced job settings or by using a PowerShell script.  Link to Powershell Script
  • If you enable or disable the Exclude deleted file blocks setting for the existing job, Veeam Backup & Replication will apply the new setting from the next job session.
  • Excluding user-specified files and folders requires Enterprise edition licensing.
  • The option to exclude swap file blocks was available in previous product versions but was enhanced in v9 to also exclude hibernation files.

*You could manually reclaim before each backup using a tool such as sdelete from SysInternals but this will inflate thin-provisioned virtual disks and temporarily consume all available free disk space on the volume.

 

Sources:

  1. https://helpcenter.veeam.com/backup/hyperv/dirty_blocks.html
  2. https://www.veeam.com/blog/save-backup-storage-using-veeam-backup-replication-bitlooker.html

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