In-depth Insight into Data Storage & Recovery on Mac System

Mac computers use its proprietary file system – Hierarchical File System (HFS). So, data storage and recovery on Mac actually relies on the HFS file system. Now, this article will discuss about this in detail.

When it comes to storing data, file system is undoubtedly one of the most crucial factors. All data storage media, including hard disk drive, solid state drive or USB flash drive or memory card, etc., are working depending on file system. Perhaps the majority of users know that Windows-based PCs format their hard disks with New Technology File System (NTFS) file system. Unlike this, Macs applies its own file system – Hierarchical File System (HFS).

In-depth Insight into Data Storage & Recovery on Mac System

Therefore, in one word, data exist on basis of the HFS file system on Macs. Plus, when any files are damaged, like PST corruption, on Mac systems, data recovery will be performed depending on the structure of HFS file system as well. Now, in the followings, we will lead you to learn such file system in detail and depth.

Main Components of Hierarchical File System (HFS)

  1. Volume Header: It virtually contains the data about the allocation block size and the location of Meta files.
  2. Allocation File: In fact, it is a bit map tracking and recording the allocation status of every block of the volume.
  3. Catalog File: It’s an extremely important component. It describes the folder and file structure on the volume. In other words, it contains all the metadata about the files on the Mac.
  4. Extents Overflow File: It contains the additional extents that are recording which allocation blocks are allocated to which files. Also, the newer versions of HFS file system improve its ability, allowing it to store extents recording the bad blocks, which can block file system from allocating bad block to file.
  5. Attributes File: It is  responsible for recording the information when booting from a non-HFS system.
  6. Journal File: It tracks and holds the information about all blocks which are updated during read/write operations.

Data Recovery on Mac System

As what mentioned above, in contrast with NTFS, data recovery of files from HFS

File system is very different as catalog file can get overwritten much sooner than that on NTFS. Usually, data recovery on Mac will go through the following steps.

  1. First off, access the volume header.
  2. Then, locate the journal file through the volume header.
  3. Next, analyze the journal file.
  4. Later, find the catalog file by recognizing the corresponding B-tree nodes.
  5. After that, on the catalog file, analyze the records of lost or damaged file.
  6. Lastly, data recovery can start from the records right away.

Author Introduction:

Shirley Zhang is a data recovery expert in DataNumen, Inc., which is the world leader in data recovery technologies, including corrupt mdf and outlook repair software products. For more information visit

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