On Thu, April 15, 2004 9:15, Gordon Henderson said:

On Thu, 15 Apr 2004 robin-lists@robinbowes.com wrote:

quoted

Does this look feasible? Can you see any major gotchas? Any better
suggestions?

Personally I'd keep life simple at the expense of a little disk space - my
layouts are also based on wanting to split partitions to, so I'd never put
/, /usr and /var on the same partition - historical reasons, including
fsck time and maybe a distrust of very old PDP11 Unix systems...  (Yes,
I'm a boring old fart) Anyway what I do with my own machines (and those I
build for others) is as follows:

I do the same thing. I thought that I could create separate partions on
top of the RAID-5 array, like I would with hardware RAID (I have some
experience with a Compaq SMART-2P and external storage rack). If that's
not the case then I shall re-think accordingly.

Partition each disk identically. That way, if you need to swap out a
drive, you already have a copy of what it's partition table ought to look
like by simply looking at the other drives - sort of self documenting if
you like.

Makes sense to me.

So for a single disk system it might look like:

  sda1	256MB		/
  sda2    1GB		swap
  sda3    2GB		/usr
  sda4  Rest of disk	/var

Actually, /usr might be less and swap would be double memory, but you get
the jist - use the 4 primary partitions and usually no more. In olden days
consideration would be made to where the disk head spends most of its time
- here, oscillating between the /usr (programs) and /var (data) might be
optimal, but I don't think anyone cares about this these days.
(historically, /usr was where users home directories lived too, then the
head would be between /usr and swap and /bin with special programs having
the 'sticky bit' set to make them reside in memory or swap to make them
quicker to load)

Partition the drives similar to this in a RAID system too. Then combine
them as follows:

  sda1 and sdc1:	RAID 1		/
  sda2,b2,c2,d2:	RAID 5		swap
  sda3,b3,c3,d3:	RAID 5		/usr
  sda4,b4,c4,d4:	RAID 5		/var

You "lose" 2 partitions: sdb1 and sdd1. You can combine these in another
RAID1 if you like, but it's not much use for anything.

OK, I get the picture.

Putting swap on RAID5 probably isn't optimal, but if your machine is
swapping heavily, buy more memory. If you are really tight on disk space
and know you have plenty of RAM no swap is probably better than too little
swap.

I'll probably put the swap on a mirror, i.e. RAID-1.

You might need to adjust the sizes of the swap and /usr partitions - I
usually aim for 2GB under /usr (that would be 4 x 768MB partitions under
RAID5) - I've found that to be enough for Debian and X and space for other
stuff, but YMMV. Remember with a 4-disk RAID 5 system you get 3 times the
capacity.

Debian also puts /home under /, so I always remove it before creating any
users and create a /var/home and symlink /home to /var/home.

If it's just a home server and you don't anticipate the log files growing,
you may want to consider not having a separate /var partition and mounting
that as /home instead...

I usually create several partitions and put as much as possible on
separate file systems, e.g. /var, /home, /usr, /opt, /tmp,
/var/qmail/queue. I might reconsider that if I have to do the same on
every disk!

I may even look into using EVMS so I can configure all of this with a
common interface.

You need to make sure you can actually boot off sdc1 should you ever lose
sda. This is vitally important! Most SCSI controllers allow you to change
the boot drive, so it shouldn't be a problem, but it might mean manual
intervention should you need to reboot it in a degraded mode.

I'll do some tests to make sure I can do this.

I've not used a /boot partition for about 8 years now. As far as I'm aware
it was just a "hack" when BIOSes couldn't boot from cylinders > 1024, and
putting / on the very first partition sorts this anyway. /boot on my
servers is just a directory under / on all my machines.

Yeah, probably. I just do it as a matter of habit now. It doesn't cost
anything, other than an additional partition.

Knowing that you are only using 4.3GB drives, I might be tempted to merge
the /usr and /var partitions.

How do you mean?

Thanks,

R.

-- 
http://robinbowes.com