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===Preventing fragmentation===
Preemptive techniques attempt to keep fragmentation at a minimum at the time data is being written on the disk. The simplest is appending data to an existing fragment in place where possible, instead of allocating new blocks to a new fragment.
Increasing a file system's [[cluster size]] decreases potential fragmentation. This is due to the fact that, having larger clusters, files are needed to split into smaller number of units to be stored. It is not without a drawback, however, as large cluster sizes increase [[slack space]]. Although, this space can be considered as room for the files to extend to without causing additional fragmentation.
Many of today's file systems attempt to preallocate longer chunks, or chunks from different free space fragments, called [[extent (file systems)|extent]]s to files that are actively appended to. This largely avoids file fragmentation when several files are concurrently being appended to, thus avoiding their becoming excessively intertwined.<ref name=mcvoy-extent/>
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