HFS Plus
The file system HFS Plus or - commonly - HFS , is a further development of HFS. It is the default file system for Macintosh computers and iOS devices and can be used for all internal and external storage media. In the operating system itself, it is referred to as Mac OS Extended and his predecessor HFS as Mac OS Standard.
The later added journaling extension ( abbreviation jHFS ) is active by default in current Macs and is also suggested when hard drives & Co. should be formatted. How about the free file systems ext3/ext4, XFS and ReiserFS or commercial NTFS from Microsoft, so it has higher stability against file systems that do not use journaling (FAT16 and FAT32, ext2, HFS, and others).
The allocation units from HFS are smaller than in FAT16/32. This can result in a higher efficiency at the partition or in partition management and access speed.
Compatibility
Unix-like operating systems
Among the Linux distributions to read and write from HFS / HFS is often by simply mount possible if the kernel supports the hfsplus filesystem; otherwise the software packages are still hfsutils ( HFS only ) and hfsplus available for subsequent installation. For write support, it may be necessary to hfsprogs to install or disable the file system journal. Also for BSD systems there are corresponding software packages. This means that the data can be read on the disk of UNIX / Linux systems when the appropriate kernel support has been installed.
Microsoft Windows
HFS is not supported by from House of Windows, but can be used under the NT - based Windows operating systems using commercial programs.
- TransMac of Acute Systems
- MacDrive of MediaFour
- HFS for Windows by Paragon Software Group
- MacOpener from DataViz ( development set )
In addition, there is a free way for read access with HFSExplorer.
From Boot Camp 3.0, which is included with Mac OS X 10.6, it is also possible to read access to HFS Plus file systems.
Mac OS X / Classic
The Classic environment in Mac OS X requires an HFS formatted system partition, the UFS filesystem is not supported.
Fragmentation
HFS and HFS are designed so that they are looking for the largest free block of memory on the hard disk, in which a file is to be saved. Only when a file does not fit into the largest free memory block, the file is divided ( fragmented), and the unwritten part is stored in another block.
Such an approach assumes that when writing a file on the forehand whose size is known. This is Mac OS X often given because the system libraries are designed to process documents so that they atomically update files in the rule: When you save a change in the current version of the document is written in one go in a new file, then the previous version is deleted and transferred the file name to the new file.
In addition, it avoids Mac OS X, reuse freed memory blocks of deleted files, if possible. Starting with Mac OS X 10.2 also the debiting of free blocks is delayed to summarize the reservation of several small blocks in a single debit of a large contiguous block.
This fragment avoidance will not work if files grow slowly, later more blocks are appended so after first creating a file. As of version 10.3 Mac OS X can therefore also at run time defrag ( on the fly defragmentation ). When opening a file, it is checked whether it is fragmented into more than eight parts. If this is the case and all of the following conditions shall apply in addition to, the file is moved to a sufficiently large free space and defragment this way:
- The file is opened by a single process.
- It lies on a recordable medium.
- The file size is more than 20 MiB.
- Within the last minute, the file was not changed.
- The operating system has been running for at least three minutes.
Another method, which is used in Mac OS X 10.3, is the independent grouping of intensively used files (adaptive hot file clustering ): By continuously keeping of statistics on the frequency of read accesses to each file identified Mac OS X, the most heavily used files and moves them into an area of the file system, which is located directly behind the central metadata. With this shift, the files are defragmented and come to rest, so that the hard disk head movements are minimized in the immediate vicinity of the most frequently used elements of the HFS file system. The intensity of use of a file is determined by dividing by the total size of the file the number of bytes read within an observation window of the last 60 hours. As a storage area for these files 0.5 % of the total capacity of the file system is being used. The number of files in this section is limited to a maximum of 5,000, and only files that are at most 10 MiB large take part in the proceedings.
More defragmentation methods are not part of Mac OS X. Apple does not recommend to use programs for subsequent defragmentation because the use is not worth usually.