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

[Damian Menscher]

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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