ReFS - Spaceless synthetic full backup

[MichaelG7]

Hello,

even though the repository seems to be acknowledged as ReFS (FastClone for Syntethic full is enabled), the "Spaceless full backup technology" (described here: https://www.veeam.com/blog/advanced-ref ... suite.html) does not seem to work.

The syntethic fulls need the same amount on the disk as active fulls.
This is not just the folder size (as shown in the article) which displays greater size than the data blocks really need, the whole ReFS is used..

Does anyone have a clue how to enable the spaceless synthetic full to safe space?

Best regards!

[Gostev]

Hello - nothing to enable there, it just works out of the box on ReFS volumes. You should review your situation with support. Thanks!

[billcouper]

Hi Michael,

The first thing you will notice is that in Windows Explorer, or any other place where you can see file size, is that all VBK are showing as the full size even though they may have been 'fast cloned'.
This is because nothing, including Windows Explorer, can show you the actual disk usage (unlike Windows NTFS Dedup, which shows you total size as well as size on disk, REFS shows you total size only).

If you get properties for everything in the volume, the total size should be more than what Disk Management says is in use on the disk - because 'properties' is counting all the 'fast cloned' files at their reported size which isn't true.
Note that you will only see a difference if your backup chains have multiple full backups. The first VBK in a chain will be full sized, subsequent VBK's will be 'fast cloned' and report the full size but only consume a fraction of the disk space.
Even if you don't have multiple VBK's in your backup chain, the 'fast clone' operation is still fast, saving massive amounts of time on the backup window.

Even though Veeam knows this is a 'spaceless' operation to create a 'fast clone' backup file, it doesn't always apply the correct logic when calculating space.
Example: You have a 1TB backup volume. You have a 1TB server that backs up to a 500GB file. You have increments as well, so there is only 200GB disk space remaining. Veeam will fail to 'fast clone' because there isn't enough space to perform the 'spaceless' operation, as it expects to require 500GB but there is only 200GB available. If you are having this problem there is a hotfix available for U3 and U3a that you can request from support, it fixed this problem for me here.