This dialog is available from the Advanced page of the configuration editor. Select Splitting... in the Compressed section.
Enable this feature to limit the maximum size of any ZIP file created. When a ZIP file is larger than the size you specify here it will be split into multiple parts. Each part will be renamed to have a number on the end of the filename. For example, if your compressed ZIP name is "Backup Job 1.zip" and it gets split into 2 parts, you would end up with "Backup Job 1.zip.001" and "Backup Job 1.zip.002". In the event you need to restore from this split ZIP file, you must first re-combine the split parts.
This feature is especially useful if you are using the remote backup feature by e-mail. Many e-mail providers have a limit on the maximum size of an attachment they will accept.
When backing up to a CD or DVD and the size of your backup exceeds the size of a single disc, Safe Data Backup will span multiple discs. In this case, the split preferences specified in this dialog will be ignored. Safe Data Backup will automatically determine the best size to perform the split, based on the size of your backup media. For more, see Backup to CD or DVD.
Backup Configurations - Advanced Properties