We recommend a minimum of 80GB disk space. If the disk is split between partitions see the below as a guide line.
 
The following directories are required for install of VT Docs:
 
/etc - systemd files, configuration files (httpd)
/var - Logs, Application data if PostgreSQL is installed locally
/opt (or /home for Ubuntu) - VT Docs install directory including application logs, backups and install files (rpm)
/tmp - VT Docs needs write access to install, run scripts (Backup/Restore, etc.). The application also needs to create temporary files when users run scans.
 
Most Linux systems come with the above directories under '/' the root filesystem. However, some come with the above directories partitioned.

If it is the case that any of the above directories are partitioned by default or for security reasons, you need to be sure the partition has enough disk space.
 
As stated in the "Minimum Requirements" document linked below, we recommend 80GB of disk space. If you have partitioned the above directories we recommend the following disk space for each partition.
https://support.visiblethread.com/hc/en-us/articles/360039245032-VT-Docs-Minimum-Requirements-for-On-Premise-deployments

/opt - Install directory 30GB+
/var - Logging, PostgreSQL 30GB+
/etc - systemd and Config files 5GB+
/tmp - tmp files and backups 15GB+