The Journal, containing incomplete transactions on the file system.Startup file, intended for non-Mac systems without HFS+ support.Attributes file, a B-tree which functions similarly to the Catalog file, but handles extended attributes (xattrs) and other attributes.Extents Overflow file, a B-tree containing supplementary information about the location of storage allocated to files.Catalog file, a B-tree containing information about the hierarchical structure of files and folders.
Allocation file, a bitmap (‘volume bitmap’) for the whole partition recording whether each allocation block is currently allocated or not.The other file system metadata is gathered into ‘files’: There are also location and size information about the other ‘files’ containing file system information, such as the catalog file.
WHAT IS HFS FILE SYSTEM FREE
There are also some summary figures for the whole volume, such as the total number of files and folders on it, and the number of unused allocation blocks (which tells you the amount of free space). Because of the importance of the Volume Header information, an identical copy is kept at the end of the partition, where it’s known as the Alternate Volume Header – just as with GPT Headers for the whole disk.ĭata contained in the Volume Header include attributes for the whole volume, the location of any journal (if that volume uses journalling), its date of creation, and so on. This explains why, as far as HFS+ is concerned, the terms partition and volume mean essentially the same thing. The Volume Header contains information about the whole partition, which makes it an HFS+ volume only one HFS+ volume can go into each partition. At the end of the partition is the Alternate Volume Header, and another area of reserved space. After that, the file system metadata and data can be anywhere within the partition. That of an HFS+ file system within a partition is much more flexible: there’s some reserved space at the start of the partition, following which is the Volume Header. Each partition then can have its own file system, of which the traditional one for Macs is Macintosh Extended, generally known as HFS+ as it is the successor to the original Mac file system HFS (Hierarchical File System).
WHAT IS HFS FILE SYSTEM SERIES
The first article in this series of three explained the basic division of storage into partitions, with a GUID partition table.
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