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Re: [Q] Is this true and does it mean there is dynamicmentation in ext2/3?

On Sat, 18 Jun 2005, Theodore Ts'o wrote:
On Fri, Jun 17, 2005 at 06:28:03PM -0400, Maurice Volaski wrote:
You don't need to defragment ext2/ext3 because as you use the
filesystem file blocks and inodes are moved around and reallocated
to keep the data nearly contiguous. It's not perfect, but it works
fairly well and you should almost never see a performance
degradation caused by the filesystem's fragmentation.

Is this statement accurate and does it mean ext2/3 is performing a sort of dynamic defragmentation?

Ext2/3 has advanced algorithms to make sure that the blocks that are allocated avoid fragmentation, but it is not doing any kind of dynamic moving of blocks/inodes.

It's probably worth noting that SGI's XFS filesystem has a userland program to eliminate fragmentation: fsr (file system reorganizer). It basically works by copying files around, and depending on the underlying filesystem to allocate contiguous blocks for the new copies of files. It's a neat hack to allow you to defrag a drive without needing too much kernel-mode involvement.

Of course, you probably would need some special stuff to ensure inode numbers don't change (NFS depends on them for filehandles, etc).

Damian Menscher
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