The Pane Time Machine

Time Machine Basics

Time Machine is the name of Apple’s technology to automatically create backup copies of your computer’s hard drives. Backups are created silently in the background each hour, and outdated file sets are automatically removed, keeping hourly backups for the last day, daily backups for the last week, and monthly backups until the destination device is full. Each backup set contains a nearly complete snapshot of the contents of all disks for which Time Machine has been activated. “Nearly” means that Time Machine automatically omits files which are considered unimportant or which can be recreated, like log files, the Trash, caches, the Spotlight search index, etc. Although the entire system can be restored for each point in time for which a backup is available, Time Machine technically stores the differences between two subsequent backup operations only (incremental backup). Differences are handled at the file level, i.e. if a single byte in a file X has changed, the entire file X will be copied during the next Time Machine backup run.

General Notes when Working with the Time Machine Pane

Time Machine can be configured to work with multiple destination disks at the same time. The destination can additionally be defined not to be a disk drive, but a server in the network, like a Time Capsule, a Mac running macOS Server, or a NAS with Time Machine support. TinkerTool System automatically detects your configuration and always works on the Time Machine destination that is currently defined by macOS to be the “active” one. The name of the destination is shown at the left bottom of the Time Machine pane (Active Time Machine disk). If you replace Time Machine disks while TinkerTool System is running, you can press the button Rescan at the right side of the pane to ensure that the application learns about the possibly changed active disk immediately. In most cases, TinkerTool System will detect this automatically after a short time. You cannot change from within TinkerTool System which destination disk Time Machine currently considers the active one, however.

If your Time Machine destination is network based, press the button Connect to network disk to let macOS connect to your backup. You cannot use any of the Time Machine features until the connection is made. To disconnect later, press the button Eject network disk. You should only disconnect if no Time Machine operations are currently running.

TinkerTool System automatically tries to determine if a backup operation is currently in progress. In this case, the warning message A backup or other Time Machine operation is currently running. is shown at the bottom of the window. Although it is usually safe to use other Time Machine features during this phase, we don’t recommend to do this, because the two simultaneously running operations could slow down each other, causing significant performance problems.

It is also recommended to disconnect from a network-based Time Machine backup volume when you completed your work with Time Machine features in TinkerTool System. The application needs to perform some monitoring tasks in the background while the network connection is active. This could slightly slow down the program and your network, especially if you are using WiFi.

Maintenance After Replacing a Data Source of Time Machine

The incremental backup strategy mentioned in the introduction only works if Time Machine can be absolutely sure which files did change between two subsequent runs and which did not. If there is the slightest doubt that a file might no longer be identical to the file Time Machine saw during the previous run, the file needs to be copied completely again in the next run.

When the identity of your computer changes, for example if you purchased a new one, or if it had to be replaced during a repair, Time Machine has to assume that all files of your computer did change, even if you have used some other copy or “cloning” application to transfer all files from the old to the new computer. This means that during the next Time Machine run, all files need to be copied again, although you did manually take care that all files are the same as before. Only if you use Time Machine itself to perform a full restore operation of the previous data, Time Machine will “know” that it can safely reuse the previous incremental backup.

The very same problem arises if you replace a volume of your Mac, but didn’t use Time Machine, but something else to copy the data back. Replacing a volume can mean

Only if you copy a disk drive or partition physically (by a copying the raw data blocks, not file by file), and if you make sure that the operating system where Time Machine is active doesn’t mount both volumes simultaneously, Time Machine will seamlessly continue its incremental operation. In all other cases, it also has to assume that all files on the entire affected volume have changed and so they need to be fully copied again.

TinkerTool System can help here, letting you manually confirm to Time Machine that a computer or a volume should still be considered the same, although its identity changed. This way, the new item will take over the role of the replaced item, and its history in Time Machine can be continued without requiring a full new backup.

Inheriting a Time Machine Backup Set from a Replaced Computer

If you need to confirm that Time Machine can safely take over a backup set that was created by a different physical computer or by a different operating system installation on the same computer, you can reassign the backup set to your current system. You should only do this in the aforementioned scenario, where all files have indeed be copied to the new system installation by some other means (not under control of Time Machine). Perform the following steps to do this:

  1. Open the tab item Maintenance on the pane Time Machine.
  2. Press the button Assign a foreign backup to this Mac….
Maintenance after replacing Time Machine data sources
Maintenance after replacing Time Machine data sources

TinkerTool System will guide you through all steps of the procedure. You will need to locate the foreign backup set to complete the operation. In case of a local Time Machine disk, this will be the top folder of the backup set. It has the name of the previous computer and is located in the folder Backups.backupdb on the destination disk. For a network-based backup, you will need to connect to the file service hosting the backup first. Here, the backup set is stored in a sparsebundle disk image. It also bears the name of the previous computer.

Depending on how Time Machine was configured before inheriting the foreign backup set, you might need to re-enable Time Machine on the Time Machine pane of System Preferences and change the backup destination.

In case the local volumes of the current computer are different from the ones of the previous computer, inheriting the backup set alone won’t be sufficient. You will additionally need to reassign each volume, which is shown in the next section.

Associating a Replaced Volume with a Volume in the Backup Set

As outlined in the introduction, there can also be cases where you need to confirm to Time Machine that it can safely take over the history of a volume in the backup, although the identity of the original source volume has changed. You can reassign a volume in the backup (for all snapshots recorded by Time Machine) to match a volume of your current setup. You should only do this in the aforementioned scenario, where all files have indeed be copied from the previous volume to the new volume (not under control of Time Machine, so Time Machine did not “notice” this). Perform the following steps to do this:

  1. Open the tab item Maintenance on the pane Time Machine.
  2. Press the button Confirm a copied volume to replace a previous volume….

Three items need to be specified:

TinkerTool System reassigns that volume for the entire time line recorded in that backup set, i.e. for all snapshots. It does not matter if the previous volume changed its name during the recorded time period. Time Machine identifies the volume correctly tracking its internal history data.

Attention Do not abuse the two maintenance features to manipulate the backup in any other cases that have not been mentioned here. The backup set could become unusable.

Backup Verification and Statistics

TinkerTool System gives you access to internal check features of Time Machine. You can learn more about the actual storage size the individual snapshots need, and you can initiate a verification run on selected snapshots, making sure that the contents of the backup is still intact.

Computing Statistics on the Change Rates between All Snapshots

As mentioned in the introduction, Time Machine simulates that each snapshot contains a complete copy of all data that was part of the backup at the recorded point in time. So if your computer always stored approximately 500 GB of data on its disks and 50 snapshots have been recorded by Time Machine, the destination volume appears to virtually contain 500 GB 50 = 25,000 GB of data. This large amount of data is not really stored on the disk, however. In reality, Time Machine optimizes storage space on its destination disks by recording only changes between subsequent backup runs. To estimate the storage space that is usually consumed by each snapshot, it can be helpful to evaluate the changes between backup runs and to compute the average rate of change. To do this, perform the following steps:

  1. Open the tab item Checks on the pane Time Machine.
  2. Press the button Compute Statistics.

Note that all files on the entire Time Machine disk need to be analyzed for this computation. This will take a considerable amount of time.

TinkerTool System creates a text report after Time Machine has completed the computation. This report can be saved to a text file if necessary.

Features for backup verification and statistics
Features for backup verification and statistics
Verifying the Contents of a Volume Snapshot

To be absolutely sure that the backup copy of a volume for a specific point in time can be read without problems and is fully intact, you can force Time Machine to validate its internal checksums. As of version 10.11 of the operating system, Time Machine protects each file in the backup by computing and recording a checksum for the content of that file. To verify a backup run for a volume, perform the following steps:

  1. Open the tab item Checks on the pane Time Machine.
  2. Use the pop-up button Snapshot to select the time of the backup that should be checked.
  3. Use the pop-up button Volume to select the volume in the snapshot that should be verified.
  4. Press the button Verify selected backup.

The check will need a considerable amount of time. If problems are identified, TinkerTool System will show a table with all errors after the verification has been completed. The table will list the full paths of the files in the backup which failed the test. There can be two types of problems, indicated as follows:

Computing the Actual Storage Size of a Volume Snapshot

In addition to the change rates between subsequent snapshots, it can be interesting to know the actual storage size consumed by a snapshot that contains the backup copy for a specific volume. Due to the internal optimization of Time Machine, this size can be very different from the simulated size for the related backup folder shown in the Finder or by similar applications listing files.

To let Time Machine compute the true storage size of a volume snapshot, perform the following steps:

  1. Open the tab item Checks on the pane Time Machine.
  2. Use the pop-up button Snapshot to select the time of the backup that should be evaluated.
  3. Use the pop-up button Volume to select the volume in the snapshot that should be evaluated.
  4. Press the button Analyze selected backup.

TinkerTool System summarizes the size value in a message that will be shown after the computation has been completed.

The actual storage size can be zero if the contents of the selected volume did not change between subsequent backup runs.

For additional features related to verifying Time Machine operation and the size of snapshots, please also see the chapter The Pane Diagnostics.

Retrieving Time Machine Logs

macOS records a log file each time a Time Machine backup has run and a new snapshot was created. These logs are usually invisible, but TinkerTool System can retrieve them for each snapshot if required. Among other information, the log discloses data

The logs are only available in English, no matter what language you have chosen for the user interface. The reports are created by macOS, not by TinkerTool System, so their contents can change without notice depending on which operating system version has created them.

To open a log for a snapshot of your Time Machine backup set, perform the following steps:

  1. Open the tab item Logs on the pane Time Machine.
  2. Press the button Select snapshot… to select the time of the backup that is of interest.
  3. Press the button OK.
  4. Confirm to macOS that its helper program authopen should have permission to read the log.

TinkerTool System shows the contents of the log in the text area at Backup Log.

Access to Time Machine logs
Access to Time Machine logs