Time Machine: Time Machine gained support for APFS snapshots with macOS High Sierra. Terminal can be used with the tmutil command to create snapshots. If you’re using a drive with APFS, you have a few options available for creating and managing snapshots. If you’re using any other file system, such as HFS+, APFS snapshots will not be available. Creating SnapshotsĪPFS snapshots are only supported on drives using the APFS format. You still need a dedicated backup that keeps data stored on a physically separate device. The point being, don’t rely on snapshots as a backup. Drive having some type of errors? The snapshot is likely experiencing the same problem. Accidently erase the startup drive and the snapshot is gone as well. That makes snapshots vulnerable to any issues the volume may encounter. They don’t exist anywhere but on the same startup drive as the data you’re trying to protect. First up, snapshots are part of the startup drive. Seems pretty good, but snapshots have a few downsides. On the surface, it looks like snapshots perform the same function as a backup, but have the added advantage of being quick and easy to create, as well as providing the ability to use a snapshot to recover from a problem quickly.
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Unwinding a snapshot can be a difficult process, as the system needs to go through each data block and remove the preserved setting, decide if the data block still contains active information, and free up the data blocks that aren’t currently in use where it can. Rolling back to a snapshot is also quick just the metadata needs to be restored since all the actual information in a snapshot data block was never changed. Only the volume’s metadata is being copied, so the process is lightning-fast, especially when compared against conventional backups. Creating a Snapshot and Rolling Back a Snapshot is FastĪ big advantage to snapshots is how quickly they can be created. However, if the block is marked as preserved, such as when a snapshot has been generated, the old block remains and is not freed up for use.Įditing a file can significantly magnify the amount of space being used, as the old versions of the file are retained in the snapshot, while outright deleting a file frees up no space at all since the snapshot will retain all the preserved data. Normally the old data block can then be marked as free and available for use. When there’s a need to write data, such as when you’re editing a file, a new data block is used to hold the changes you’re making, instead of writing the data back to the original block. Snapshots leverage the APFS’s copy-on-write system. Time Machine can create and manage APFS snapshots for you. In this guide, we’re specifically dealing with the APFS snapshots. APFS-based snapshots use an entirely different mechanism even though Apple has continued to use the “local snapshot” nomenclature for both types of file system snapshots. Note: Apple has supported local snapshots on HFS+ formatted drives since OS X Lion. At the moment a snapshot is taken, there’s no increase in the space used on a volume. A snapshot essentially marks all the currently used data blocks on a volume to be preserved that is, no changes can be made to them. When a snapshot is initially created, it takes up no additional space on the volume. Snapshots Take Up No Space, But Can Magnify the Amount of Data Blocks Used In this Rocket Yard guide, we’re going to take a look at APFS snapshots, how they’re created, managed, and deleted, as well as the advantages and disadvantages of snapshots.
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Before the system update is applied, a snapshot is taken of the startup drive, ensuring that if something goes wrong with the update process, you could recover from the problem quickly and be back right where you were before you started the system update. Apple makes use of the snapshot feature whenever a system update is performed.
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