Combined root, /var and /usr (was: cvs commit: src/sys/conf kern.post.mk)

[Greg 'groggy' Lehey]

On Monday, 12 September 2005 at  9:55:18 -0700, David O'Brien wrote:
> On Mon, Sep 12, 2005 at 02:58:42AM -0700, Colin Percival wrote:
>> Emanuel Strobl wrote:
>>> Hmm, why was default size of root changed to 500M?
>>
>> Because I was increasing the sizes of /tmp and /var at the same time; because
>> I know that some users do somehow manage to fill up /; and because re@ told
>> me to. :-)
>
> Perhaps we should follow what SGI and Sun has done for years on its
> workstations: a combined / + /var + /usr. 

I've been recommending and doing this for years.  FWIW in the fourth
edition of "The Complete FreeBSD" I recommended 4 to 6 GB; I'd now say
that 8 to 10 is better.  I also recommend a separate /var if you're
doing important things with it.  Here's what I have on my two main
machines:

=== root at wantadilla (/dev/ttyp0) ~ 98 -> df
Filesystem     1048576-blocks   Used Avail Capacity  Mounted on
/dev/ad0s1a              9912   4211  4908    46%    /
/dev/ad0s3h             51895  41842  5902    88%    /home

=== root at echunga (/dev/ttyp4) ~ 29 -> df
Filesystem        1048576-blocks   Used Avail Capacity  Mounted on
/dev/ad0s1a                14873   7985  5698    58%    /
/dev/ad0s1g                 9916   3846  5276    42%    /home
/dev/ad2s1h               188356 106658 66629    62%    /src

/src contains source files, including multiple FreeBSD source trees.
I see that on echunga / is now 15 GB, but that includes a large /var,
and it's still only just on 8 GB.

> We would make it 15GB and be done with it.  My laptop has a combined
> /+/var+/usr of 12GB and I have multiple kernels installed and room
> in swap for a crashdump.

Note that this could also mean that you don't need to install the
kernel; if you build it in /usr (on the root file system), you can
link to it directly in the kernel build directory.

> No need to reply you hate this idea - just one opinion that there
> are other partitioning schemes (especially now that we have a
> dynamic /) successfully used.

In CFBSD IV I explain how / and /usr came to be: about 32 years ago,
they had / on an RK03 (0.5 MB), so they *had* to put the rest of the
system somewhere else.  The fact that we still use a separate /usr has
something to do with the reliability of the Seventh Edition file
system and something to do with not changing the way our grandfathers
did things (writing "return (FOO)" instead of "return FOO" is
another example).

Greg
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