The Pane APFS

Overview on APFS Volumes

As explained in the previous chapter, Apple’s File System APFS uses modern techniques for storage organization that can be confusing upon first look.

The tab item Overview on the pane APFS tries to present the individual objects that have been created as part of APFS technology on the available hard disks, focusing on their hierarchical relationships. It shows the complete list of all APFS data structures on all disks currently attached to your Mac. By using the disclosure triangles in the column Object Type, the individual elements can be expanded and their parts can be reviewed. The following technical terms are used:

The relationship between the different APFS object can be visualized as hierarchy
The relationship between the different APFS object can be visualized as hierarchy

When you click on a line in the table, details about identification and size will be shown in a box at the lower part of the window. The table is updated automatically when connecting or disconnecting APFS disks. This also happens when you alter the APFS configuration, e.g. with Disk Utility. APFS volumes still appear in the table even when they are currently not mounted.

If you are working with multiple partitions or if multiple disks are connected to your Mac, the space in the table might not be sufficient to get a clear overview. To get a better view in this case, click the button Separate window. The APFS overview will then be shown in a resizable window which can be extended to the whole screen if necessary. Keeping the overview window open can be especially helpful if you like to work with critical APFS operations, e.g. copying one disk to another one (see below).

The APFS table can be shown in a separate window to get a clearer overview.
The APFS table can be shown in a separate window to get a clearer overview.

Please note that an APFS container can be spread onto multiple physical devices. This can be the case, for example, if a container is stored on an Apple Fusion Drive, a composite disk made by software, comprised of an SSD and a mechanical hard drive. For a Fusion Drive, the disk considered “faster” is shown with the type Main, the slower but bigger disk is marked as Secondary.

APFS volumes may have a special label that assigns this volume a particular task. This additional entry is called APFS role. At the moment, Apple uses the following types of roles:

Working with APFS Snapshots

The purpose of snapshots has been discussed in detail in the chapter for the pane Time Machine already. Each Local Snapshot of Time Machine is implemented technically by an APFS snapshot. However, the operating system is free to use these snapshots for purposes other than Time Machine as well. The tab item Snapshots on the pane APFS gives you the opportunity to work with all snapshots, not only the ones in use by Time Machine.

However, Apple does not grant users the right to create new APFS snapshots on a volume at their own discretion. There is no official feature to initiate this process for a selected volume, unless this is performed by backup software which has explicit approval by Apple to do so. The user can produce new APFS snapshots only indirectly, by sending a maintenance command to Time Machine to create a Local Snapshot. However, this is naturally associated with the restriction that snapshots will be created on those APFS volumes only which are part of a Time Machine backup, and that snapshots will be created on all those volumes simultaneously.

If you like to create APFS snapshots in this indirect way, click the button Create new snapshots via Time Machine… in the lower left corner of the window.

APFS snapshots can be listed and deleted
APFS snapshots can be listed and deleted

To review the current snapshots stored for a specific APFS volume, perform the following steps:

  1. Open the tab item Snapshots on the pane APFS.
  2. Choose the desired volume with the pop-up button Select APFS volume:.

The complete list of snapshots will then be shown in the table. When you click on a line in the table, more detailed information will also be shown in the box at the bottom of the window. You will see the name of the snapshot as it was assigned by macOS, a short numerical identification, also known as XID, and a unique identification in form of a UUID. The field private size indicates how much storage space the corresponding snapshot is actually consuming for itself. Virtually, each snapshot contains a copy of the entire volume for a particular point in time of the past, which is much more storage. However, the snapshot shares this storage with the current volume content or other snapshots. Such multiply counted storage is not actually used additionally, so it does not become part of the private size of a snapshot.

The notice Limiter is an indicator that macOS is also using this snapshot as additional marker to define the minimum size of the respective APFS container. The operating system is capable of changing the size of partitions in hindsight, without requiring to erase and to re-partition the entire disk. When using APFS, reducing the size of a partition means shrinking the APFS container included in that partition. Because multiple volumes and multiple snapshots may share the storage space of a container, shrinking can be a complex procedure. The “rearmost” APFS snapshot of the container determines the minimum size to which the container can be reduced. The detail box lists this furthest limit for each snapshot as tide mark.

Due to the fixed width of the control window of TinkerTool System, it can sometimes be difficult to see all data about the snapshots without clipped fields. When you click the button Separate window, TinkerTool System will copy the contents of the table into a resizable window. You can set an arbitrary width for this window, making sure all table columns can be shown without limitations.

When you have selected one or more snapshots in the table, the button Delete can be clicked to remove the respective snapshots immediately. The visible data on the APFS volume won’t change in any way. Only the possibility to travel back in time at the push of a button to an earlier state of the volume will be eliminated. The button Delete all… will remove all APFS snapshots from the volume after you have expressly confirmed this.

Copying APFS Data

macOS offers system features that make it possible to copy parts of an APFS hierarchy, i.e. containers, volume groups, or volumes, very rapidly. This quick-copy function is known as replication in this context. The resulting copies will match the originals with high fidelity. Each copy is an identical clone of the original and will also retain volume names. The unique identifiers won’t match, of course.

In detail, you can clone the following APFS objects:

It is possible to clone an entire installation of macOS Big Sur. The operating system and your user data are stored in a volume group consisting of a volume with the role System and a volume with the role Data. If that system is currently running, there will also be a sealed snapshot volume for the system volume. At least two additional volumes with the roles Preboot and Recovery also need to be copied. TinkerTool System and macOS automatically detect whether you intend to replicate a macOS installation and automatically add the minimum set of volumes required. This is only guaranteed to work correctly if the following conditions are met:

Attention Unfortunately, a successful replication of all required macOS volumes does not always mean that the copy can launch correctly, or could launch on any computer.

In all cases, source and destination must belong to different APFS containers. This means it won’t be possible to duplicate a volume within its container.

APFS objects can be copied quickly
APFS objects can be copied quickly

Perform the following steps to copy an APFS object:

  1. Open the tab item Snapshots on the pane APFS.
  2. Choose the object that should be copied in the table Source. If desired, set a check mark at Copy snapshot instead of live volume additionally.
  3. Select the destination where the object should be copied in the table Destination.
  4. Click the button Copy….

While selecting source and destination, TinkerTool System will already show a message at the lower edge of the window that gives a preview which operation would be executed if you started the procedure. If data will be lost in the target container (because one or more volumes replace already existing volumes), you will be informed in a separate dialog and will have to confirm this. When copying a snapshot, you will also be asked about the snapshot’s name.

When the copying has begun, a dialog sheet will be shown which is filled with a report of the ongoing operations. After the copy procedure has completed, the report can be saved or be printed.

By clicking the Stop button, TinkerTool System can be forced to cancel the running copy operation. This is not recommended however, and should only be used in emergency cases. At the moment, macOS is not mature enough yet to handle an APFS volume copied “halfway”. In the destination container, the volume will appear as damaged item with a temporary name. In such a case it is recommended to restart the computer, and then to remove the affected volume from the destination container with Disk Utility.