tunefs question

[Richard Noorlandt]

Hi everybody,

While reading a bit about tunefs I noticed that UFS reserves 8% of the drive
space for the root user and the system. However, I don't really understand
what this space is actually used for. From the tunefs man page I understand
that it is primarily used to guard against fragmentation, and that's about
it. Is this the only thing that the reserved space is used for?

I'm building a large array for my fileserver, and it actually hurts a bit to
see that so much space is "wasted" without a very clear reason to do so.
Especially because the data on the array won't be modified very often, it
appears to be quite a lot of disk space just to prevent fragmentation. Does
anybody have some more information on this?

And while I'm at it: what is the effect of the expected average file size
option? What are the benefits and dangers of tweaking it? From the FreeBSD
handbook I understand that the FS actually optimizes itself as time passes,
but that's about all that's said about it.

Regards,

Richard