[CentOS] Swap space for kvm virtual host

Nataraj incoming-centos at rjl.com
Mon Mar 14 21:24:07 UTC 2011

I have a kvm virtual host running on what will become CentOS 6 with 12GB
of memory and a Quad Xeon  X5560 2.8Ghz .  The store for virtual
machines will be a software raid 6 array of 6 disks with an LVM layered
on top.  I'm not initially planning any major overcommitment of
resources, though there could be a need for some overcommitment with a
light workload on the guests.

 In recent years people seem to configure a wide range of different swap
allocations.  I was thinking initially to spread swap across seperate
non-raid partitions on 4 of these disks, but the downside of that is if
I put 2gb on each disk, then I can only swap processes that will fit in
2gb swap space.  Also, if one of the disks fails, I have to reboot if
anything was swapped to that drive.

My questions are as follows:

   1. What experience are others having with putting swap space on raid
      partitions?  I was thinking about maybe swapping on a raid10
      device, otherwise an LVM spanning multiple drives.
   2. In practice, what kinds of swap allocation are people finding
      useful for a kvm virtual host of this size?

I definitely don't want a system that is so overcommited that
performance is impacted, but if some overcommitment is reasonable for
VM's that have light workload, then I consider that.  I can increase
system resources when that becomes necessary.


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