Combined root, /var and /usr

[Nate Lawson]

Greg 'groggy' Lehey wrote:
> 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

Large / means you have to wait for it to fsck before bg fsck can run on 
other filesystems.  On my crashbox (laptop), that is unacceptable.

/var on the same filesystem as / means that you're bound to have lots of 
problems found via fsck that you may have to review manually when a busy 
system crashes.  With var separate from /, you can just blow it away 
(fsck -y) and get back to work.

If you don't have a diskless server or livecd, having a separate / means 
you can boot and rebuild a fs with fsdb.  With a combined partition, 
this is probabilistic.

If you start getting block errors on your hard drive, separate 
partitions mean you can pull off the files still alive, remap bad 
sectors, and newfs.  Try that with one large /.

> 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 

See above for examples still valid today.

> and something to do with not changing the way our grandfathers
> did things (writing "return (FOO)" instead of "return FOO" is
> another example).

I think that one is more about consistency.  return () is a keyword 
while exit() is a function.  It's the same reason we don't write if().

-- 
Nate