Deduplication restrictions

Block-level deduplication restrictions

During a disk backup to an archive in a deduplicating vault, deduplication of a volume's disk blocks is not performed in the following cases:

• If the volume is a compressed volume
• If the volume's allocation unit size—also known as cluster size or block size—is not divisible by 4 KB

  Tip: The allocation unit size on most NTFS and ext3 volumes is 4 KB and so allows for block-level deduplication. Other examples of allocation unit sizes allowing for block-level deduplication include 8 KB, 16 KB, and 64 KB.

• If you protected the archive with a password

  Tip: If you want to protect the data in the archive while still allowing it to be deduplicated, leave the archive non-password-protected and encrypt the deduplicating vault itself with a password, which you can do when creating the vault.

Disk blocks that were not deduplicated are stored in the archive as they would be in a non-deduplicating vault.

File-level deduplication restrictions

During a file backup to an archive in a deduplicating vault, deduplication of a file is not performed in the following cases:

• If the file is encrypted and the In archives, store encrypted files in decrypted state check box in the backup options is cleared (it is cleared by default)
• If the file is less than 4 KB in size
• If you protected the archive with a password

Files that were not deduplicated are stored in the archive as they would be in a non-deduplicating vault.

Deduplication and NTFS data streams

In the NTFS file system, a file may have one or more additional sets of data associated with it—often called alternate data streams.

When such file is backed up, so are all its alternate data streams. However, these streams are never deduplicated—even when the file itself is.