[CentOS] Virtualization platform choice

Chuck Munro chuckm at seafoam.net
Mon Mar 28 00:34:18 UTC 2011

On 03/27/2011 09:00 AM, Jerry Franz wrote:
> On 03/27/2011 02:57 AM, Jussi Hirvi wrote:
>> >  Some may be bored with the subject - sorry...
>> >
>> >  Still not decided about virtualization platform for my "webhotel v2"
>> >  (ns, mail, web servers, etc.).
>> >
>> >  KVM would be a natural way to go, I suppose, only it is too bad CentOS 6
>> >  will not be out in time for me - I guess KVM would be more mature in
>> >  CentOS 6.
>> >
>> >  Any experience with the free "VMware vSphere Hypervisor"?. (It was
>> >  formerly known as "VMware ESXi Single Server" or "free ESXi".)
>> >
>> >  http://www.vmware.com/products/vsphere-hypervisor/overview.html
>> >
>> >  I would need a tutorial about that... For example, does that run without
>> >  a host OS? Can it be managed only via Win clients? Issues with CentOS
>> >  4/5 guests (all my systems are currently CentOS 4/5).
> I'm currently using Ubuntu Server 10.04-LTS as a host for KVM running
> CentOS5.5 guests I migrated from VMware Server 2. Works fine. A nice
> feature of current generation KVM is that you are supposed to be able to
> do live migration even without shared storage (although I haven't tested
> that yet). I wrote some custom scripts to allow me to take LVM snapshots
> for whole-image backups and I'm pretty happy with the who setup.
> The only corners I encountered were
> 1) A lack of documentation on how to configure bridging over bonded
> interfaces for the host server. It turned out to be fairly easy - just
> not clearly documented anyplace I could find.
> 2) The default configuration for rebooting/shutting dow the host server
> just 'shoots the guests in the head' rather than having them shutdown
> cleanly.:(  You will want to write something to make sure they get
> shutdown properly instead.
Once in a while I find it's useful to compromise just a little, so I use 
Scientific Linux 6 as the Host OS, and run a bunch of CentOS-5.5 Guest 
VMs.  It all simply works.

KVM has improved quite a bit, and the management tools work well.  One 
thing that requires a bit of skill is getting bridging configured (which 
I simply did by hand from the RHEL-6 documentation).

I'm happy with the result, and see no reason to replace the underlying 
SL-6 Host distro.

SL-6 as the Host is rather slow to shut down gracefully and reboot, 
because it hibernates the Guest OSs, one at a time, rather than just 
killing them.  Hibernation takes a while to write out to disk if you've 
assigned a lot of RAM to the Guests.  Bootup has to restore the saved 
state, so that's a bit slow too.  But it works very well.

I use partitionable RAID arrays for the Guests, and assign a "raw" md 
device to each one rather than using the 'filesystem-in-a-file' method. 
  It seems to be a bit faster, but there's a learning curve to 
understanding how it works.

One thing I found a bit annoying is the very long time it takes for a 
Guest to format its filesystems on the RAID-6 md device assigned to it. 
  That's mostly due to array checksum overhead.  RAID-10 would be a 
*lot* faster but somewhat less robust ... you pick what's best for your 
own situation.


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