Normally, a file system will allocate disk blocks based on a time
vs space algorithm. By having blocks free in a number of locations,
the best location to allocate the disk block due to the growing
of fragments or just a new block can be realized. A couple of factors
in determining this is interleave, rotation speed, time to seek, etc.
Once the file system's free space decreases to a specified point, the
allocation then just allocates blocks due to their availability. My
guess, is that 5% is the point where this tradeoff is made.
Mitch
========
Stephen C. Tweedie wrote:
>
> Hi,
>
> On Tue, 13 Jul 1999 09:38:30 +0000, Thierry Vignaud
> <tvignaud@mandrakesoft.com> said:
>
> > Miquel van Smoorenburg wrote:
> >> The reason that 5% of disk space is reserved is to always have some
> >> room left. The ext2 allocation algorithm needs this to prevent
> >> fragmentation.
>
> > I think the main reason is to let the sysadmin to fix the system in case
> > of problem and to prevent users from filling all the free space.
>
> Partly that...
>
> On Tue, 13 Jul 1999 15:52:31 +0400 (MSD), "Khimenko Victor"
> <khim@sch57.msk.ru> said:
>
> > And you can NOT use this room for conf files editing (unless you are
> > root, of course)... No, main reason is to give ext2fs defragmentation
> > algorithm space to breathe.
>
> Most config files _are_ edited by root, but ext2 defragmentation is an
> equally good reason.
>
> Why does one reason have to be wrong? If we have two valid reasons for
> doing something, do we have to own up to only one of them?
>
> When we added this stuff it was primarily for fragmentation, but we were
> fully aware of the fact that it would be a failsafe for root at the same
> time. They are both good reasons for keeping a reserved portion.
>
> --Stephen
>
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