Data Loss in HFS and Recovery

HFS or Hierarchical File System is a file system. It was developed by Apple for using in their computer systems running on MAC OS. It was originally designed for using in hard drive and Floppy, but it is also used in read only media like CD-ROMs.

HFS is the advanced version of MFS file system. It partitions a volume into logical blocks, each of 512 bytes. These blocks are then grouped into allocation blocks. These allocation blocks may contain one or more logical blocks depending on the size of volume. There are 5 structures that make an HFS volume: -

1. Logical blocks 0 or 1 are the boot blocks. These blocks contain startup information of the system like name of the shell and system files.
2. Block 2 contains MDB (Master Directory Block). It defines a number of data regarding the volume like data and time stamps when it was created, location of other volume structures like volume bitmap and size of logical structures.
3. Block 3 is starting block of Volume Bitmap. It keeps record of which allocation block is free and which are in use.
4. The Extent Overflow File is the B-tree. It contains extra size that record which allocation block is allocated to which file.
5. Catalog File is an added B-tree that contains records for all the files and directories stored in the volume. Files and directories in the catalog file are stored by their unique Catalog Node ID (CNID). It stores four types of record.

• File Thread Record that stores just name of the files and the CNID of its patent directory.
• File Record that stores a number of metadata about the files including its size, CNID, timestamps, resources forks and pointers to the files. It also stores two 16 bits fields for use by the finder.
• Directory Thread Record that stores name of the directory and CNID of its parent directory.
• Directory Record that stores data like the number of files stored in a directory, timestamps, CNID of the directory.

This is the storage mechanism of HFS file system. The main part of the HFS is the catalog file. It keeps the record of all the files and directories stored on the drive. If any type of the corruption occurs in these files, the file system may damage. In such conditions, the hard drive may become inaccessible and operating system can’t read data from the drive. It may lead to the critical situation of data loss. In these situations, to recovery your lost data, Mac data recovery software is required.

Data recovery mac software helps user in recovering the data from corrupted or damaged logical volumes in Mac operating system. These software use advanced algorithms in searching for the lost data from the particular volume on which data loss occurred. You can simply use this software by installing it on a healthy computer and attaching the corrupted hard drive to it.
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