[CentOS] CentOS 6 Partitioning Map/Schema

Fri Sep 2 16:03:24 UTC 2011
Devin Reade <gdr at gno.org>

You've already received some good responses so I won't rehash a
lot of what was said.  However here are few more comments without
a lot of backing detail (but it should give you enough info to
google for detail):

1. Despite the RedHat link someone provided, I think the advice of
   putting almost everything on the root filesystem is a lot of
   bunk, at least for servers.  The old arguments for separate 
   filesystems still apply.  I suspect that the single filesystem
   perspective is coming from desktop scenarios, and especially
   laptop users and those coming from MS Windows.

2. Putting /boot on its own filesystem and using LVM for everything
   else is a generally good idea from both the management and 
   snapshot perspectives as someone previously described.  However be
   aware that most (if not all) LVM configurations will disable
   write barriers -- this is probably mostly of interest for when
   you're running a database.  You need to put on your combined 
   DBA and sysadmin hat, have a look at your underlying disks, 
   disk controller, filesystem stack, database, UPS/powerfail
   monitoring, and budget to see where your balancing point is.
   Yes, I have databases on LVM on top of RAID on top of SATA;
   but it's better to know your risks rather than having them
   be a surprise.

3. Pay attention to whether your disks are using the old 512 byte
   sector size or the new 4k sector size (sometimes called advanced
   disk format), and whether or not your disks lie to the OS about
   the sector size.  The RAID, other MD layers, and filesystem
   need to know the truth or you can run into performance and/or
   lifespan issues.

4. Regarding swap: Yes, having it is still a good idea under most
   circumstances.  The old "2 * physical memory" rule no longer applies.
   Follow the sizing guidelines from RedHat that someone posted.
   The kernel is smart enough to use it when necessary and avoid it
   otherwise.  Having it can get your server through unusual circumstances
   without crashing but you should have enough memory that you're not
   paging under normal circumstances.  See also point #6.

5. Consider encrypting swap.  See crypttab(5), including the comments
   about using /dev/urandom for the key.

6. Putting /tmp on tmpfs is a good idea in that it ensures that it
   gets cleaned out at least when the system reboots.  (Running cron
   jobs to clear it out periodically can cause problems; under some
   circumstances.)  This is a good argument to have swap; you can
   use tmpfs without a significant impact of /tmp using up physical
   RAM.  Also see the 'tmp' option in crypttab(5).

7. Under CentOS 5 having less than 2G for /var could cause problems
   with updates, especially between minor versions.  I've increased
   my minimum to 4G under RHEL6 due to kdump concerns.