Compression level is recommended if you use plan to store backup files and VM replica files on storage devices that support hardware compression and deduplication.
Is an optimized compression level for very low CPU usage. You can select this compression level if you want to decrease the load on the backup proxy.
Is the recommended compression level. It provides the best ratio between size of the backup file and time of the backup procedure.
Compression level provides additional 10% compression ratio over the Optimal level at the cost of about 10x higher CPU usage.
Compression provides the smallest size of the backup file but reduces the backup performance. We recommend that you run backup proxies on computers with modern multi-core CPUs (6 cores recommended) if you intend to use the extreme compression level.