Disk optimization
In the past, many Mac users have relied on disk optimization to improve access times when reading files from a hard drive. As files are changed and the hard drive fills up, parts of a single file may be stored in different locations on the volume. In other words, the file becomes fragmented. Disk optimization streamlines the physical locations of files by collecting file fragments and putting them back together in contiguous parts of the drive. Rearranging files (and metadata) improves data access times and minimizes the time required to move the hard drives read/write head. However, if a failure (such as power loss) occurs during optimization, files can be damaged, and you will need to restore them from a backup copy.
Once you have migrated to Mac OS X, you may not need to optimize your disk at all.
Heres why:
Hard disk capacity is generally much greater now than a few years ago.With more space available, the file system doesnt need to fill up every nook and cranny.
The Mac OS Extended (HFS+) file system format avoids reusing space from deleted files as much as possible.This avoids prematurely filling small areas of recently freed space.
Mac OS X v10.2 and later versions include delayed allocation for volumes that use the Mac OS Extended format.This design allows a number of small allocations to be combined into a single large allocation in one area of the disk.
Fragmentation was often caused by continually appending data to existing files.With faster hard drives and better caching, as well as changes to the ways applications work on Mac OS X, many applications simply rewrite the entire file each time. Mac OS X Panther can also automatically defragment such slow-growing files.
Aggressive read-ahead and write-behind caching means that minor fragmentation has less effect on perceived system performance.
Mac OS X systems have hundreds of thousands of small files, most of which are rarely accessed. Optimizing them is a major effort for very little practical gain.There is also a chance that one of the files designated for rapid reads during system startup might be moved during defragmentation, which would actually decrease performance.
For all of those reasons, there is usually little benefit to defragmenting a hard drive on a Mac OS X system. However, if your disks are almost full and you often modify or create large files, theres a chance they could be fragmented. In this case, they might benefit from defragmentation. A number of third-party utilities are available for this purpose.
