Changes to keychains, volume structure, Time Machine, Migration Assistant, and the security command tool that have only recently come to light, six months later.
Time Machine
Tahoe 26.4 broke the copying of login keychains. Apple has at last explained how you can copy them successfully, and what backup software needs to do. Explained in full.
For the last 38 days, I have been measuring free and used space in my Mac’s boot container and its backup storage. Here’s what has happened, and how upgrading to macOS 27 changed it.
Although they can only grow in size, and mustn’t be left lying around, snapshots can be very useful, provided you manage them carefully, as described here.
How do you locate part of a document that you removed or changed greatly, and copy that content into the version you’re currently editing? What to do when it’s too much for Undo.
Caching to disk improves performance, but cached data are optional and may be purged when additional free space is needed. This explains how that’s performed by the deleted service.
Major improvements in its plots make this new utility even better for tracking changes in used space, and so forecasting how long backup storage will take to fill.
Further tests on two volumes with over 90 GB purgeable space. One took almost 30 minuted to become available, the other never got there at all. The log reveals who was responsible.
Snapshots made by Time Machine and tmutil should be purgeable, although sometimes they won’t purge, and aren’t shown reliably as purgeable space. An exploration of bugs and missing documentation.
If you leave your Mac running overnight, but not sleeping, what does it do? Does it perform maintenance tasks that it would otherwise have to do during the day?
