I've recently done an in-place Windows 2012 R2 to Windows 2016 upgrade on all my Veeam servers, and upgraded Veeam to v9.5. My aim is to utilise the new ReFS block pointer efficiencies so that synthetic fulls don't take all day. Under Windows 2012 R2 my jobs were using full weekly backups with Windows Dedupe crunching them down, but with ReFS I'm expecting a similar deduplication effect as part of the file block linking.
As part of the upgrade, I deleted all local backups (from within the Veeam interface "disk" section) to clear out the historical database. I then formatted the local RAID disk with ReFS (4k allocation size), and then kicked off active-full backups of all my jobs.
All my Veeam servers save their backup files to a local RAID disk (via a local repository setup within a local scale-out repository, so I can add further disks in the future without having to change the destinations in the jobs).
This weekend saw the first synthetic full triggered, and I'm not seeing what I expected I would.
One job has about 3.7TB of backup files to crunch through (1 active-full followed by 3 incrementals). The repository is configured to save each VM as a separate file.
It is still running now and has been for 2 hours and is only 39% through the synthetic full creation. Taskmanager shows the disk at 100% active time with about 200MB/sec reading and writing going on.
Also another job which has finished (took 55 minutes to make the synthetic fulls of 11 VMs), had 396GB of backup files (1 active-full followed by 4 incrementals). The resulting 372GB of synthetic fulls are shown as taking 372GB of disk space when viewing the file properties. The whole backup folder shows 768GB size, and 768GB size on disk in folder properties.
I was under the impression that quite a bit of the synthetic fulls would show up as taking no disk space as the matched blocks would just be pointers in the existing backup files.
One thing to note, I have the repository settings set to allow 8 concurrent tasks. However I don't think that is an issue since the 3.7TB job is the only one running now, and still the disk is at 100% active time.
So with the above information is it possible to know if ReFS is doing its thing right? and if not, what step did I miss when reformatting the disk?