cvs commit: src/sys/conf kern.post.mk

[Robert Watson]

On Tue, 13 Sep 2005, Garance A Drosehn wrote:

> I must admit I'm a little uneasy moving /usr and /var into '/', just 
> because I'm so used to the way it is.  I really *like* having /var as a 
> separate partition.  But hard disks are huge compared to how they used 
> to be, so I don't mind having a 500-meg '/'.  I *do* save the 
> kernel.debug information in my /boot/kernel's, and my root partition is 
> still under 50% full.

We probably ought to move this discussion to another list, but -- I 
remember two very specific occasions where I first realized how important 
an isolated /var is:

(1) In about 1995, when I first started using ppp, I discovered the
     hard way that the default logging level was set a bit high, and filled
     the entire hard disk with log records in a couple of days.  Don't
     remember which FreeBSD revision that was.  It's amazing how little
     time it takes, if you get a log messsage ever second or so, to fill up
     a hard disk.

(2) Whenever it was that Outlook started becoming really popular, and all
     e-mails became word files or power point presentations -- bandwidth
     was high, but disks weren't large enough to put up with that.
     Especially with single sender multiple recipient spamming of word
     files.

In both of these cases, having an isolated /var meant that /tmp didn't 
fill, so new /tmp files could still be created.  Today that would be the 
difference between being able to SSH into the machine or not, because SSH 
requires inodes and directories to be allocated by default when you log 
in.

While sizing becomes a continuing problem with multiple partitions, having 
them offers some important isolation of software faults.  The main 
"problem" is that the strength of isolation is a bit too high.  If we 
supported live resizing and relocation of partitions, it would be less of 
a serious constraint.  The problem people have now, and the reason that 
installkernel installing debuggin symbols is an issue, is that recovering 
from an early poor (or simply dated) choice about partition sizing is very 
difficult.  While 300GB disks may be commonplace and affordable today, the 
layout choices for 4GB disks haven't gone away yet.

Robert N M Watson