[mythtv-users] Mythbacked on ESXi 5.0

Raymond Wagner raymond at wagnerrp.com
Mon Oct 24 17:41:38 UTC 2011

On 10/24/2011 12:46, Tom Hill wrote:
> On Mon, 2011-10-24 at 11:27 -0400, Raymond Wagner wrote:
>> On 10/24/2011 04:29, Tom Hill wrote:
>>> On Sun, 2011-10-23 at 20:55 -0700, Govindarajan wrote:
>>>> I am trying to comprehend the advantages of such a set up but I am not
>>>> getting convinced. One could just run Mythtv (front and backend) on a
>>>> physical box. Running more than just backend VMs or multiple backends
>>>> on the same physical box could be one. Could you explain the other
>>>> advantages please?
>>> People running separate file storage, router/firewall applications can
>>> have them all on the same hardware.
>>> m0n0wall, Vyatta, pfSense, FreeNAS, openfiler, etc. will all run very
>>> happily in a virtualised environment.
>> But the question is _why_ would you want to?  One has to seriously
>> question the sanity of the person who uses virtual machines so they can
>> run half a dozen border firewalls on the same machine.
> <misguided-rant/>

You gave the example of running all those tasks in a virtual 
environment.  M0n0wall, Vyatta, and pfSense are all border firewalls.  
You pick one that provides the features you want, and you use that.  You 
don't run multiple different versions, or multiple instances of each 
version, running in VMs.  You want it as simple as possible.  Complexity 
leads to mistakes, which leads to vulnerabilities, something you 
absolutely don't want on your border firewall.

FreeNAS and Openfiler are both software NAS solutions.  Now first, I'm 
ideologically against running such a thing on the same hardware as a 
border firewall, back to the whole complexity thing.  That aside, as 
before, you pick one that provides the features you want, and you use 
that.  There is nothing to gain from multiple redundant instances on the 
same hardware.  Beyond that, putting them in a VM on a shared machine 
would require they have dedicated access to that storage.  Another VM on 
the same machine would not be able to simultaneously access it.  Should 
you try to run a storage appliance on the same host hardware as your 
backend, your backend would have to access the storage over the 
virtualized network interface, even though the disks it is accessing are 
local, leading back to the question as to why you would ever want to run 
such a thing in a VM.

>> There are really four specific cases to run a virtual machines:
>> You use a virtual machine because you need to run multiple independent
>> kernels.  Para-virtualization doesn't require the same environment, but
>> it does require everything be run on the same kernel.  If you've got
>> some applications that need Linux, other that need Windows, and still
>> others that only run some ancient blend of HPUX or some such, full
>> virtualization is your only option.  Well, that or just running multiple
>> servers.
> Like FreeBSD (m0n0wall/pfSense)? Windows? Solaris? Plenty of people are
> using Nexenta/OpenIndiana for ZFS storage on their LANs.

Yes.  I'm saying this _is_ a valid reason for wanting to run a virtual 
machine.  However, for most home users, you can simply select different 
different software that serves the same purposes.  With proper hardware 
selection (HDHomeRun), you can run MythBackend on Nexenta/OpenIndiana 
for ZFS use.  Alternatively, you can run ZFS on FreeBSD, which opens up 
the option of using any Linux USB capture devices with webcamd.  Or, you 
can run Linux with the zfsforlinux filesystem drivers.

>> You use a virtual machine for development work.  Either you need to run
>> a completely different architecture, or maybe you just simply want to
>> isolate development work from your workstation so its not disruptive
>> against other applications you've got open.
> Sure, why not. I'm aloud to, right?

Yes.  Again, I said this is one of the valid uses.  However very few 
MythTV users are actually doing development on MythTV, or even testing 
out versions before putting them straight into production.

>> So where does this get you with MythTV?
> Nothing more, nothing less. That's the point. Well, except maybe less
> power.

It gets you a bunch of hassle (which is less).  If it doesn't give you 
advantage in other places, then why do it?

> Maybe you live in a world where power is cheap, I don't know. Do you
> have your own fusion reactor?

I don't understand how virtualization has anything at all to do with 
power consumption.  On the contrary, virtualization necessarily adds a 
whole layer of overhead, which means higher CPU usage, and higher power 
consumption.  You can run multiple applications on a single Linux 
install without any problems.  You can use paravirtualization techniques 
to ease maintenance with dedicated disk and network space, exactly the 
same as full virtualization.  You don't need full virtualization to 
consolidate all those little systems into one big one.

What full virtualization gets you, as I seem to have failed to explain 
above, is absolute isolation between multiple virtual systems on a 
single piece of hardware.  Isolation used for stability when you're 
doing things that likely cause crashes (development), or when something 
absolutely cannot be taken down (because each second of downtime costs 
you money).  Isolation used for security, where the images are managed 
by independent groups or customers and may be compromised.  For a MythTV 
user running a production server, that just doesn't really apply.

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