Does it do incremental backups or just a complete new dump each time?
It will do full backups or different kinds of incremental: it will compare files' modification dates with archive dates: if the modification date is later the file is backed up. A different setting compares origin files' modification dates with the modification date of the backup file, if any: if the dates are different a backup is made. The program will back up in Finder format -- exact copies -- or in Stuffit format, saving space and the entire backup is one file for ease of handling. Stuffit backups can be encrypted with a password. The program will simply back up where you tell it to, overwriting previous backups, or you can set it to make a new folder for each backup, including the date in that folder's name, so every earlier backup is retained.
Whichever option you choose, the program will verify its backups either by comparing checksums or a byte-by-byte comparison of original and backup files.
Details, from the program manual:
Full: backs up all files and folders in the backup list, irrespective of modification or archive dates of the files, or existing files in the destination. This is the fastest method on a per-file basis, and the simplest where the backup is a straight file copy. In Finder format, existing earlier versions of files are overwritten if they are in the correct destination path, respecting the hierarchy and dated folder options you’ve set (see the sections on these options below. For example, no files will be overwritten if the Make Dated Folder option is enabled).
Update: backs up files that have been modified since the last time they were backed up. Does not look for files in the destination. This is the fastest method overall, and recommended for general use in a local environment. In Finder format, overwrites earlier versions of files in the same destination paths, respecting hierarchy options, unless Make Dated Folder is enabled.
Differential: backs up files that have been modified since the last Full Scope backup. As fast as Update on a per-file basis, but could copy more files, since it backs up every file that has been modified since the last full backup. In Finder format, overwrites earlier versions of files in the same destination paths, respecting hierarchy options, unless Make Dated Folder is enabled. This and Update are the recommended scopes for data that is archived off-site.
Incremental: looks in the destination (respecting hierarchy options) for files corresponding to those in the backup list. Backs up every file whose modification date in the origin is later than the modification date of the corresponding file in the destination, if one is found. If no destination file is found, Incremental backs up the origin file. In Finder format, backups overwrite earlier versions of files of the same name in the same destination path, unless Make Dated Folder is enabled. Not available in Stuffit format, since modification dates of files in the destination archive cannot be checked.
* Discussion of scope options
Every Mac file has three dates: creation, modification and archive. While the first two are set by the OS and are visible in the Finder’s Get Info, the archive date is set by backup programs. Free Backup’s scope options work by comparing different pairs of these dates:
Full backs up every file in the backup list, and then sets the archive date of each origin file to the current date. Existence of and modification dates of files in the destination are not considered. Existing backup files are overwritten if they are in the same location in the destination, respecting hierarchy options, unless Make Dated Folder is enabled.
Update compares the modification date of an origin file with its archive date. If the modification date is later, the file is backed up. Archive dates of all origin files that were backed up are then set to the current date. Existence of and modification date of any file in the destination are not considered.
Differential makes the same comparison and decision as Update, but does not revise the archive date of origin files. Thus once a Full backup has been made, and an origin file is subsequently changed, it will be included in all future Differential backups, until another Full backup is made.
To understand Differential Scope, consider this example. You manage a remote office of a large company. You have an employee handbook consisting of a loose-leaf binder with numbered pages. Periodically, headquarters sends you partial revisions of outdated material in the handbook, to replace per page numbers. To build a current copy of the handbook for a new employee, you’d find it most convenient to take a new copy of the original binder and replace all the outdated original material with a single set of pages representing all revisions since the binder was first issued, i.e. a Differential backup. For your own use, though, it would be more convenient to keep your copy up to date by adding only newly changed pages as they arrive, i.e. an Update backup.
Incremental compares the modification date of the origin file with the modification date of a file, if any, in the backup destination, respecting hierarchy options. If the origin file has a later modification date than the destination file, a backup is made, overwriting the existing destina- tion file if any. Incremental Scope does not check or set the archive date. Incremental has much the same effect as Update for local backups but is slightly slower, since FB checks the destination twice for each file: first to get the backup’s modification date to see if the original should be backed up, and a second time to verify the backed up file. Note that if you change the hierarchy options, Incremental will not see destination files as placed in the old hierarchy, and will back up these files again. Thereafter, it will only back up modified files. Full, Update and Differential operate without regard to destination hierarchy. Incremental Scope is disabled if Make Dated Folder is checked in Preferences, since that option causes the destination path to change with each backup.
In Finder format, FB offers two verification options. You can use either, both or neither.
Checksum verification sums the number of bytes in each file as it is selected for backup. After each file is backed up, the number of bytes of destination files are summed and the two totals are compared. Equivalence is a precise indicator that the entire backup was successful. If the two totals do not match, an error dialog informs you. Checksums, equivalent or not, are given in the log entry for that backup, if the log is enabled in Options.
Extensive: makes a byte-by-byte comparison of the data in each origin and backup file. This check is highly exact and is thus slower, especially for large files, but enhances security of data in critical uses.