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How many reserved blocks are needed to avoid ext4 filesystem fragmentation?

ie flag

On a typical ext4 filesystem, 5% of blocks can only be allocated by privileged processes. According to the manpage of tune2fs:

Reserving some number of filesystem blocks for use by privileged processes is done to avoid filesystem fragmentation, and...

The default of 5% can become a sizable chunk of disk, in modern large storage systems. Although this may seem like a lot, ensuring that data on a very large filesystem does not fragment may just as well require 5% of that very large filesystem. On the other hand, it could be that a specific size is enough, regardless of the size of the filesystem itself.

Q: Is it possible to give a rule of thumb figure for the minimum number of blocks that is needed to avoid fragmentation?

vidarlo avatar
ar flag
It would depend *entirely* on the use mode of the file system. A lot of large files changing continuously? A lot of small files? Static data written once and read thereafter? How full is it? If it's 80% free anyway, the amount of reserved obviously doesn't matter - and so on.
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