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| Keywords: File system fragmentation.svg Example of how file systems become fragmented The following is from the article of the same name on Wikipedia A blank disk has 5 files A B C D and E each using 10 blocks of space for this section a block is an allocation unit of that system it could be 1K 100K or 1 megabyte and is not any specific size On a blank disk all of these files will be allocated one after the other Example 1 on the image If file B is deleted there are two options leave the space for B empty and use it again later or compress all the files after B so that the empty space follows it This could be time consuming if there were hundreds or thousands of files which needed to be moved so in general the empty space is simply left there marked in a table as available for later use then used again as needed Example 2 on the image Now if a new file F is allocated 7 blocks of space it can be placed into the first 7 blocks of the space formerly holding the file B and the 3 blocks following it will remain available Example 3 on the image If another new file G is added and needs only three blocks it could then occupy the space after F and before C Example 4 on the image Now if subsequently F needs to be expanded since the space immediately following it is no longer available there are two options 1 add a new block somewhere else and indicate that F has a second extent or 2 move the file F to someplace else where it can be created as one contiguous file of the new larger size The latter operation may not be possible as the file may be larger than any one contiguous space available or the file conceivably could be so large the operation would take an undesirably long period of time thus the usual practice is simply to create an extent somewhere else and chain the new extent onto the old one Example 5 on the image Repeat this practice hundreds or thousands of times and eventually the file system has many free segments in many places and many files may be spread over many extents If as a result of free space fragmentation a newly created file or a file which has been extended has to be placed in a large number of extents access time for that file or for all files may become excessively long Rfc1394 File systems Megabyte | ||||
