Free space needed for backup


What is the amount of free space needed to make a backup?

Is it 2 x backed up volume?

I’m currently at 40-45% used space on / , /tmp is also on /, and backup is failing at Creating final backup archive … archive failed!

I am assuming that the backup script way of working is: copy files to /tmp > copy tmp to tar > delete files from /tmp … is that correct? Is there any workaround for this, apart from excluding files/folders from the backup and manually moving those files? I even tried to backup to ssh to a server with 20 x my needed space, but the source server still runs out of space…


For the backup process, tar is used to backup the user’s home directory – and the tar file creates the new tar archive in /tmp.

The files aren’t copied out of /home/username, tar works on /home/username and creates a new file in /tmp.

However, if you’re seeing space issues, you may want to ensure that it’s only doing one backup at a time, copying those to your final destination, and delete the temp file, and then start on the next backup.

To do that, make sure that the “Transfer each virtual server after it is backed up” option is selected on the backup options screen.

With that option set, the amount of space you need in /tmp to make a backup should be roughly the amount of space that your largest domain uses.

However, also note that you can go into Webmin’s advanced options, and change the temp directory used, that may also solve your problem (that’s in Webmin -> Webmin -> Webmin Configuration -> Advanced Options).


Thanks for the reply!

I already moved the temp directory in /

What happens is: 1-start the backup, with / at 45% use ( out of 55GB total), 2- waiting for backup to finish and keep watching df and seeing / increasing it’s use until 100%, 3- I get archive fail cat: write error: No space left on device, 4-df and now / is at 68%, and there is an incomplete backup.tar.gz file (of ~12GB).

It means this is either a bug somewhere, or the backing up process needs about ~40GB for an under 20GB backup…


Yikes, that’s no good!

Just to clarify, what kind of backup is it that you’re performing there? Is that a Virtual Server backup, as configured in Virtualmin -> Backup and Restore -> Scheduled Backups?

Or is it a different kind of backup that you are performing?



I’ve put a screen shot:


Hmm, the backup destination there is of possible concern… it’s tough to tell since it’s blacked out, but is that backup destination actually inside one of your Virtual Servers?

If so, you may want to move that outside of any of your Virtual Servers.

Another thought –

It looks like your backup file type is setup as “One large file”, which can require quite a bit of space while generating the backups.

Would it be an option to use “One file per server”? That would require considerably less space while creating the backups.



Backup location is /home/backup/backup.tar.gz, which is outside any virtual server space.

I could set it to “one file per server”, however one server is ~20GB and the other under 400MB, so it’s unlikely that it’d make any difference.

Hello, any other input?