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I'm running Debian 6.0.5 (squeeze) with ext3 as the filesystem. I'v read that ext3 does not require defrag, but I was recently trying out some torrent clients and they all came with the allocate disk space before downloading option checked. I downloaded some files in each client, removed it [the client] via aptitude, moved the data around, downloaded stuff with the other client... I was wondering if all this mess wouldn't cause some disk fragmentation, even under ext3. If so, how could I run a defrag?

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The ext file system family is much more efficient than most filing systems. In a short answer. No, ext3 is efficient enough that it can handle large pieces of data.

If you want the long version and more reasoning read this article.

The key difference illustrated there is that FAT (and NTFS?) lumps modifications to files as well as new files one after another. Whereas EXT spreads the files more freely across the disk so that modifications can occur close to the original data, thus avoiding fragmentation.

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up vote 0 down vote accepted

Although a disk defragmentation might not have been needed, there were still some "empty" files left behind occupying disk space because of the allocate disk space before downloading option.

Those files can be found using the Disk Usage Analyser tool, found under Applications > System tools.

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Checking View > Allocated Space will show allocated space and unchecking it will show only "occupied" space. So by comparing both you can see which blocks are larger when Allocated Space is checked - this indicates which folders have files allocating disk space so you can delete them.

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