![]() This allows unrelated files to fill in the empty spaces left behind.ĭefragmentation is the operation of moving file extents (physical allocation blocks) so they eventually merge, preferably into one. However, most filesystems do not write the new file in the same physical place on the disk. Updates are a common cause of this, because in order to update a file, most updaters usually delete the old file first, and then write a new, updated one in its place. Some groups of files may have been originally installed in the correct sequence, but drift apart with time as certain files within the group are deleted. For instance, a group of files normally read in a particular sequence (like files accessed by a program when it is loading, which can include certain DLLs, various resource files, the audio/visual media files in a game) can be considered fragmented if they are not in sequential load-order on the disk, even if these individual files are not fragmented the read/write heads will have to seek these (non-fragmented) files randomly to access them in sequence. When a file has many extents like this, access time for that file may become excessively long because of all the random seeking the disk will have to do when reading it.Īdditionally, the concept of “fragmentation” is not only limited to individual files that have multiple extents on the disk. Repeat this hundreds of times and the filesystem will have a number of small free segments scattered in many places, and some files will have multiple extents. Add a new block somewhere else, and indicate that F has a second extent (see example 5 in the image).This presents the same problem as in the previous example: if there are a small number of files or not much data to move, it isn't a big problem, but if there are thousands or even tens of thousands of files, there isn't enough time to move all those files. Move all the files after F until one opens enough space to make it contiguous again. ![]() The file could also be so large that the operation would take an undesirably long period of time. This would not be possible if the file is larger than the largest contiguous space available.
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