Maintenance of snapshots on backup storage is more complicated and currently opaque. Although uncommon, this can occur when Macs are unable to make full backups because they’re disconnected from their backup storage for more than 24 hours at a time. Even so, TMA snapshots can become orphaned and left indefinitely, for the user to spot and delete manually. The rule it applies is inflexible: it deletes any local snapshots (on a volume being backed up) that are more than 24 hours old, unless it’s the last snapshot on that volume, which it retains for this backup. The next issue for TMA to tackle is whether the backup to be used is inherited using machine store inheritance normally that shouldn’t be needed, allowing TMA to proceed to snapshot maintenance.īefore making any snapshots for this backup, TMA performs housekeeping on its own previous snapshots, both on each volume being backed up, and on the target volume (backup storage). However, those are written to the log, where they are a useful reference in the event of performance problems. These tests are also performed when backing up to network storage, when they may fail altogether, but TMA appears to proceed regardless of the results. In more recent versions of macOS, file write performance to the target volume is then measured by writing a single 50 MB test file, and concurrently writing 500 files of 4 KB size to the volume. ![]() It’s at this stage that the next of multiple target volumes is identified when backups are being rotated between different destinations. If that’s not available, then TMA will normally still make and maintain local snapshots of the volumes to be backed up. First is the mount point of the backup storage, referred to as the target volume. In the log and starts checking the resources it needs to do that. Once backupd has been told to make a backup, it announces Although normally very reliable, failure of those subsystems will prevent backups from taking place. Should regular automatic backups fail, the first task in discovering where the problem lies is to check DAS-CTS scheduling. ![]() DAS-CTS is explained in fuller detail in this article, using TMA as an example. One simple rule applied is that the first backup made after a Mac starts up is delayed for five minutes, to allow other processes such as Spotlight indexing checks to be run first. SchedulingĪutomatic TMA backups aren’t run at fixed times, but are scheduled and dispatched by the DAS-CTS subsystems so that backups are only made when conditions are suitable. It has been a couple of years since I last examined how Time Machine makes backups to APFS: this article steps through what happens when Ventura 13.2.1 makes an automatic hourly backup of an APFS volume to APFS backup storage, Time Machine to APFS, or TMA. Time Machine has undergone major changes over the last few years, both to make efficient backups from APFS, and to support backups stored on APFS volumes.
0 Comments
Leave a Reply. |