Understand how TM backs up and how snapshots work to minimise the size of local snapshots and backups, and the time they take. How to ensure files in iCloud Drive are backed up properly.
APFS
First securing the Home folder in an encrypted sparse disk image, then to whole-volume encryption using CoreStorage, now using T2 and Apple silicon chips.
How to tell whether someone has been eating the (APFS) porridge on one of your disks, using Get Info and DiskUtility’s First Aid. And a surprise hidden volume from 3 years ago.
The only disk images of varying size used to be sparse bundles and sparse disk images. Now plain read-write disk images can also vary in the disk space they take, as explained here.
When do sparse files explode to full size, and how could you preserve them in transit? Can you copy clones or snapshots? How to preserve extended attributes?
Focussing on sparse bundles and UDIF read-write disk images, this explains their types, structure, how their size can change, and how fast they are in use.
APFS or HFS+? Which can Time Machine back up to? What about hard disks? Which format for use on PCs? And which are supported by Disk Utility now?
macOS has an elaborate set of rules determining which types of xattr are preserve during different types of copying, including syncing to iCloud Drive. Here they are in full detail.
Extended attributes were added to Mac OS X 10.4, and soon supported the quarantine xattr. They have since flourished, and have valuable properties.
Released in Mac OS X 10.5 Leopard on 26 October 2007, it supported Time Capsules launched in January 2008, and in Big Sur could back up to APFS.
The Eclectic Light Company 