The dump/restore utility is limited to a maximum of how many different incremental backups?

The answer is "nine".

Dump looks at documents in a filesystem, figures out which ones should be sponsored up, and duplicates those records to a predetermined plate, tape or other stockpiling medium. Resulting gradual reinforcements would then be able to be layered over the full backup.  

The restore command plays out the opposite capacity of dump; it can reestablish a full reinforcement of a filesystem. Single documents and registry subtrees may likewise be reestablished from full or halfway reinforcements in interractive mode.

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