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Jim Grisham (talk | contribs) →Types: Added sub-section on fragmentation of file system data structures |
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* Free space fragmentation
* The decrease of [[locality of reference]] between separate, but related files
* Fragmentation within the data structures or special files reserved for the file system itself
===File fragmentation===
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To avoid related file fragmentation and improve locality of reference (in this case called ''file contiguity''), assumptions or active observations about the operation of applications have to be made. A very frequent assumption made is that it is worthwhile to keep smaller files within a single [[file directory|directory]] together, and lay them out in the natural file system order. While it is often a reasonable assumption, it does not always hold. For example, an application might read several different files, perhaps in different directories, in exactly the same order they were written. Thus, a file system that simply orders all writes successively, might work faster for the given application.
===Data structure fragmentation===
The catalogs or indicies used by a file system itself can also become fragmented over time, as the entries they contain are created, changed, or deleted. This is more of a concern when the volume contains a multitude of very small files than when a volume is filled with fewer larger files. Depending on the particular file system design, the files or regions containing that data may also become fragmented (as described above for 'regular' files), regardless of any fragmentation of the actual data records maintained within those files or regions.<ref name="ntfs-reserves-space-for-mft">{{cite web |title=How NTFS reserves space for its Master File Table (MFT) |url=https://learn.microsoft.com/en-us/troubleshoot/windows-server/backup-and-storage/ntfs-reserves-space-for-mft |website=learn.microsoft.com |publisher=Microsoft |access-date=22 October 2022 |language=en-us}}</ref>
For some file systems (such as [[NTFS]]{{efn|NTFS reserves 12.5% of the volume for the 'MFT zone', but ''only'' until that space is needed by other files. ''(i.e., if the volume ~ever~ becomes more than 87.5% full, an un-fragmented MFT can no longer be guaranteed.)''<ref name="ntfs-reserves-space-for-mft" />}} and [[Hierarchical File System|HFS]]/[[HFS Plus]]<ref name="diskwarrior-hfs-hfsplus">{{cite web |title=DiskWarrior in Depth |url=https://www.alsoft.com/in-depth |website=Alsoft |access-date=22 October 2022}}</ref>), the [[Collation|collation]]/[[Sorting|sorting]]/[[Data_compaction|compaction]] needed to optimize this data cannot easily occur while the file system is in use.<ref name="windows-2000-defrag-performance">{{cite web |title=Maintaining Windows 2000 Peak Performance Through Defragmentation |url=https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-2000-server/bb742585(v=technet.10) |website=learn.microsoft.com |publisher=Microsoft |access-date=22 October 2022 |language=en-us}}</ref>
==Negative consequences==
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