Newbie Info

[John Wendel]

Ed Greshko wrote:
> John Wendel wrote:
>> aragonx at dcsnow.com wrote:
>>>> As you can gather from the other responses. defrag isn't used often on a
>>>> Linux system.  It isn't needed; the Linux kernel and friends do much
>>>> better job of allocating space on a hard disk.
>>>>
>>>> The following two sites begin the explanation.  You can explore more
>>>> from there.
>>>>
>>>> http://en.wikipedia.org/wiki/Defragmentation#_note-4
>>>> http://pl.atyp.us/wordpress/?p=241
>>> I have had several threads on this very list about this subject.  The
>>> threads went something like this (dramatization):
>>>
>>> Me:  I want to defrag my disk
>>>
>>> Everyone else:  Shut up noob.  Linux doesn't need to do that winblows M$
>>> nonsense.
>>>
>>> Me:  How could a filesystem never get fragmented.  It's not possible.
>>>
>>> Everyone else:  Go back to M$ you.  We will have none of this Linux
>>> bashing.
>>>
>>> Fast forward to today, a few years later.  I've got several file systems
>>> that are showing 20 - 30% non-contiguous as reported by fsck and I
>>> have no
>>> way other than a cp or dump to fix it.  This just doesn't seem right.
>>>
>>> The real question is not so much if there is fragmentation or not.  It
>>> is,
>>> is there a performance difference or not.  Honestly, I can't say for
>>> sure.
>>>  I don't have reliable tests from years ago as to how long it took to
>>> copy, write or read from a file to compare it to.  I can say this, my
>>> performance is not bad enough to warrant the file system dump and
>>> restore.
>>>
>>> So, in conclusion, after years of heavy usage, my file systems still
>>> perform reasonably well.  It would be nice to be able to defragment your
>>> hard drive but realistically, it isn't much needed.
>>>
>>> I hope that answers your question with real world experience.
>>>
>>> ---
>>> Will Y.
>>>
>>>
>> We haven't yet reached filesystem perfection!
>>
>> A quick google for "ext4" reveals that the file system gods think that  
>> it is worth the effort of writing a new (and incompatible with ext3)
> 
> Really?  I thought the case was....
> 
> Backward compatibility
> 
> The ext4 filesystem is backward compatible with ext3, making it possible to
> mount an ext3 filesystem as ext4 (using the “ext4dev” filesystem type).
> 
> Forward compatibility
> 
> The ext4 filesystem is forward compatible with ext3, that is, it can be
> mounted as an ext3 partition (using “ext3” as the filesystem type when
> mounting). However, if the ext4 partition uses extents (one of the major new
> features of ext4), forward compatibility and therefore the ability to mount
> the filesystem as ext3 is lost. Extents were enabled by default in the
> 2.6.23 kernel. Previously, the “extents” option was explicitly required
> (e.g. mount /dev/sda1 /mnt/point -t ext4dev -o extents).
> 
>> filesystem. The development version of the code is in the current
>> kernel.org kernel (and in F8 ???). Among its features are a new block
>> allocation scheme that keeps files contiguous and "online
>> defragmentation" (whatever that is). I assume that in a few years we'll
>> be complaining that the online defrag demon is taking too much CPU time
>> on our 64 core box.
>>
>> I amused that there is an entire industry devoted to selling software to
>> defrag winblows filesystems.
> 
> 
> 

Excuse me, I should have read more carefully. I'll shut up now :(


Regards,

John