This week I had that dreaded message for the second time. Probably due to modern GB games that patch themselves regularly and entering the Windows Insider program (so a new Windows 10 version every now and then).
The last time (quite desperate) I deleted one of recent the Data.4096.nn.dat files and did a repair. It worked but I just lost a lot of backups. So I wanted to avoid that at all cost.
What happens when the client backup drive starts filling up is that beyond a certain point the weekly cleanup task will at most only adjust the indexes and not shrink the actual cluster storage files (the Data.4096.nn.dat and Data.512.nn.dat). So even if you mark backups as to be deleted at the next cleanup it still does not free-up disk space. If the disk becomes even more filled-up, even the adjustment of the cluster indexes stops after a few backup-ed machines.
Yesterday I found a much simpler and better (and not destructive to start with)!
First and very important is not to make things worse, so do not forget to stop both backup services so no backups are added during this operation.
It turned out that using the build-in compression feature of NTFS (which happened to be enabled on my client backup drive, so probably by default), could free up the GB’s I needed to get things working again. After compressing around 64 of the smallest Data.4096.nn.dat my free space went up from 4GB to 25GB (around 6GB more that the largest file on the disk).
As my client backup drive is 2TB, I was quite happy that I did not have to compress all files.
After that it was a matter of marking old backups as ‘to be deleted at next cleanup’ and run the clean-up job. After the cleanup it’s best to revert the compression so you can do the trick again if needed.
You can apply the compress attribute by selecting a number of files and right-click them for the property dialog. There use the Advanced Button. It takes a while to compress so take some coffee or better a lunch in the meantime.
For command-line lovers, the command to look for is called compact.
Removing the compression is just a simple compact /u * command from within the Client Computer Backup directory located in ServerFolders on the Client Backup Drive.