However, matching unchanged folders have different volume numbers, as if they were stored on separate mounted volumes.
This is synthesised into what is presented by the Finder as the customary hierarchy of files and folders, just as with HFS+ backups. Apple hasn’t indicated whether this continues to be whole files, or whether only changed data are copied. File data is kept as usual in the container’s Physical Store, to which file data is copied during each backup. The volume assigned the role of Backup appears to be a regular APFS volume, and is protected from normal access, even by root. Instead, what appears to function as a form of virtual file system is created using new features in APFS. Files and folders which haven’t changed since the last backup are represented there by hard links: inspect the inode number of two corresponding ‘copies’ of a folder which hasn’t changed between backups, and you’ll see that they are one and the same, with identical inodes, just as regular file hard links are.ĪPFS doesn’t support directory hard links, so can’t use the same mechanism when storing Time Machine backups. However, to do so requires the destination APFS volume to be assigned the role of Backup, and allocation of storage space as a Physical Store.Ĭurrently, when backing up to HFS+, Time Machine creates a folder within which is a replica of the file system of the volume being backed up.
It’s not clear when Update, Hardware, Enterprise or Prelogin volumes will come into use, and some may only be available to Apple Silicon Macs, particularly as they won’t be using EFI/UEFI.Īs 9to5Mac has already reported, Big Sur is the first version of macOS which can make Time Machine backups to APFS volumes without using a virtual HFS+ file system on a sparse bundle. This means that, for the time being at least, sealing isn’t available to verify the integrity of files or the file system anywhere else, such as on the Data volume.
The System volume within a boot Volume Group is now sealed using a tree of cryptographic hashes, as I have detailed here.
This article can’t be as authoritative, but I’ll try here to outline some of the improvements which are documented in various sources, including the latest update to the APFS reference documentation.ĪPFS in macOS 11 changes volume roles substantially. Despite extensive coverage of much of Big Sur and Apple Silicon, one session was missing from WWDC, that detailing changes in APFS for macOS 11.