Re: partitioning a raid 5 disk array -

["Ben Eisenbraun" <user=82@nabble.blu.org>]

 Howdy Stephen, 

You haven't gotten many responses yet, so I'll see if I can stir the pot 
a bit. 

> The new system is dual core system - 8 G of physical ram- (four - 73 G 
> drives RAID 5) useable space of 219 ~ G .  Planning on using Ubuntu 7.10 
> server. 
> 
> Looking for insight and best practices on the partitioning scheme. 

I think opinions will run the gamut here. 

On one end of the spectrum you have The Partitioners, who create separate 
partitions for /, /boot, /usr, /home, /var, /tmp and depending on your 
specific application, maybe a /var/mail or a /opt. 

On the other end of the spectrum is the One Partition crowd, who just put 
everything on / and keep going. 

And then there are all the people in the middle.  I personally lean toward 
the more partitions camp on servers and the single partition camp on 
desktops. 

The arguments for many partitions are that they let you define different 
mount options for security/performance/policy reasons for each partition, 
you can worry less about malicious/dumb users or runaway processes filling 
the disk and killing the machine and you have some additional protection 
against file system corruption. 

The downsides are that you have to make some guesses about how much space 
is appropriate and efficient for each partition, and there is some admin 
overhead in dealing with the more complex scheme. 

For a linux web server, I'd create /boot, /, /usr and /var.  Also a /tmp 
or symlink /tmp to /var/tmp, since I don't like having the tmp directory 
on the root filesystem.  Depending on if the web server was running an 
application that did a lot of writing to disk, maybe a /web or similar 
filesystem just for the web app. 

> I am of the thought to take the "guided partitioning" offered during the 
> setup that will setup up the a file structure of  one partition - 
> everything under / and the default swap space of 8 G. 

That's certainly the easiest. 

> ( I am aware of the best practice of assigning 1.5 the space the physical 
> memory) 

I'm not sure that's a best practice any more. 

Here's the thing: swap is important because it gives the box a chance to 
survive Slashdotting or a DOS attack or a runaway process.  I would never 
configure a UNIX machine without swap. 

That said, I never want to use swap.  Memory is cheap enough that I only 
want to use swap for unusual circumstances.  If the machine is regularly 
swapping, it needs more memory or performance will suffer. 

So that said, do you really need 12 GB of swap (i.e. your 1.5x system memory 
suggestion)?  Can you envision a scenario where the machine would need to 
swap out 6 GB of httpds?  Are you going to be watching it closely enough 
that you can intervene and save the machine without a reboot anyway? 

If I had to hazard a guess, I'd say that 2-4 GB of swap is appropriate for 
most servers.  Yes, that's a sweeping generalization. 

In your particular case, since you have small/expensive/fast SCSI storage, 
I'd aim low and add swap files later as needed.  It's not hard to do, e.g.: 

dd if=/dev/zero of=/var/swap/swap.0 bs=1M count=2048 
mkswap /var/swap/swap.0 
swapon /var/swap/swap.0 

And then you put it in the fstab. 

-ben 

-- 
and the end of all our exploring will be to arrive where we started and 
know the place for the first time.                         <t.s. eliot> 

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