Why is defragmentation unnecessary?
This could be for any file system but EXT4 works.
Does Ubuntu need to be defragged like windows. Does it do this on its own.
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Most Linux file systems avoid fragmentation to begin with*, so you don't need to defrag Ubuntu under normal circumstances.
*This is accomplished in the way files are written to the disk. Mostly files are written in such a manner that they remain contiguous, with some filesystems arranging the inodes to avoid fragmentation, and when it occurs, to keep it to a minimum. Even when files are modified a lot, moved around etc, the filesystem uses the same principles to avoid fragmentation.