When this level is selected, no compression occurs for the backup task. While this will take the least amount of CPUs during a backup task, do keep in mind that it will take a significantly large amount of space to store backup files. Proxmox virtual disk images are sparsed, which means that an allocated disk image only uses some of the actual data space. The rest of the allocation is sparsed, or filled with zeros.

A backup with no compression will save the disk image without compressing the empty spaces. This will cause the backup file to take as much room as the disk image itself.