Sparse files are now common among databases, disk images, and virtual machines. How they work in APFS, how they’re created, and how they can explode.
APFS
Consider the fidelity of backup copies, the speed of a backup method, and the risk of losing the contents of that backup. And test backups by restoring samples from them.
Classic TM backed up HFS+ to HFS+; current TM backs up APFS to APFS. But what if you want to back up a mixture of APFS and HFS+ volumes?
How the resource forks of Classic Mac OS became extended attributes in Mac OS X 10.4, then flourished. How clone files handle xattrs, and which are used by APFS itself.
If the Finder’s Get Info dialog may report inaccurate total file size, does that mean the folder sizes are also incorrect? And does this affect volumes too?
How to obtain and read entries in the Unified log made by APFS. Their structure, and a guide to their identification and occurrence.
Classic Mac OS could give the size of data and resource forks. High Sierra ignored extended attributes, and Sonoma tries to add them, but only includes some.
Union mounts let you merge the contents of two volumes without copying any files. Do they work as expected in Sonoma’s APFS, though?
Other file systems, with an outline of vfs and vnodes used by the kernel, and how they’re important in checking code signatures.
This reference covers fsck_apfs, diskutil information, diskutil apfs, conversion of HFS+ to APFS, mount_apfs, and newfs_apfs.
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