[MLUG] fsck ext3

[Leslie Satenstein]

How would lvm play into this?

I am also of the opinion that a copy of a source file to a target file would result in the target file being unfragmented, or less fragmented then the source file. I understood that the file system tries to always allocate contiguously.

With lvm, we may have some quirks that aide the creation of contiguous files.

Leslie

nikosapi <me at nikosapi.org> wrote: On March 9, 2008 16:36:31 Jeremy Chapman wrote:
> Yanik Doucet wrote:
> > I'm no expert at file systems, but I always try to use quotas to keep
> > all my partitions under 80% used if possible, 90% at worst if dealing
> > with a file system containing mostly small files.  I never had any
> > problem with fragmentation using this logic (or that I am aware of..)
> >
> > I think you can also specify some switch when using mkfs.ext3 to
> > reserve a certain amount of free space.
>
> "That I am aware of" is the problem... it is insidious, the slowdown
> will be tiny, but as it accumulates over years of writes and usage...
>
>  I mean we make fun of windows for having to defrag, yet we accept speed
> degradation on our linux FSes due to the same process, and we don't even
> have a tool to deal with it! I think we have to accept that if files are
> written non-contiguously, the hard drive heads have to move more between
> reads, making reads slower.
>
> I also don't see how quotas will help with FILE fragmentation, yes it
> will help with blocks since the FS can find contiguous free space to
> write files.
>
> I wonder if the lack of a defragger for ext3 is a technical issue...
> seems to me you could do something rudimentary by looking at file
> creation times to try to group files most likely associated with each
> other together on closer sectors. From my total lack of knowledge, this
> is basically how I understood Win defraggers to work (the smart ones).
> Afaik the smart windows ones even put more often-used files closer to
> beginning of platter for faster seek times (may be a myth or not do
> anything)?
>
> I could be totally missing the concept here, would be happy to be told so
> :)
>
> Jeremy
>
> PS: the reserved blocks in ext3:
>
> "*-m* /reserved-blocks-percentage/
>
>     Specify the percentage of the filesystem blocks reserved for the
>     super-user. This avoids fragmentation, and allows root-owned
>     daemons, such as /*syslogd
>     *(8)/, to continue to function
>     correctly after non-privileged processes are prevented from writing
>     to the filesystem. The default percentage is 5%."
>
> So, how does this avoid fragmentation?

Hello Jeremy,

Have you come across http://vleu.net/shake/ in your research?
It seems safe and filesystem agnostic as well. You can use it to get an idea 
of how fragmented your files are with: "shake -pvv [dir]"

Here's more info about the program: http://tinyurl.com/2jj573