[mythtv-users] Mythbackend on VMware Server with DVB-tuners

Raymond Wagner raymond at wagnerrp.com
Sat Apr 30 19:43:29 UTC 2011

On 30 April 2011 17:20, Tyler T <tylernt at gmail.com 
<mailto:tylernt at gmail.com>> wrote:
>     > > Some say that its overkill to run virtualization at home
>     > > I have to disagree
>     >
>     > No, it's simply overkill.
>     > Anything in the userland can be completely isolated from the
>     rest of the
>     Sure it can, but it's a lot easier to use a VM. For example, how many
>     users know how to run two parallel installations of Myth on one host
>     without them stepping on the other?

For FreeBSD, you're a single Google search away from the half dozen 
commands needed to build a new world into a directory to run a Jail.  
For Gentoo, you follow the same exact stage3 install instructions you 
used to set up the system in the first place.

>     Plus, a VM is easier to back up and
>     restore separately from the rest of your system, can be moved to a
>     different host easily, and you never have to worry about an upgrade in
>     the VM breaking something on your host OS or in another VM.

On my backend, backing up a Jail is as difficult as 'zfs snapshot 
zroot/jails/mythbe at date'.  Recovery is then either a 'zfs rollback' or 
'zfs clone', change in the jail root, and restart of the jail.  Unless 
you need some special services offered by one kernel or another, there 
is no problem migrating from one host to another.  A couple years ago 
when my firewall died, I took a backup snapshot of my DNS and DHCP 
servers, copied it onto another machine, added the necessary aliases, 
and I was done.  All told it took maybe 5 minutes to bring the new 
machine online in its place.

>     At work we've saved literally hundreds of thousands of dollars in
>     hardware and
>     just as much in labor by switching to VMs for 95% of what we do -- VMs
>     are here to stay, no doubt about it.

You saved hundreds of thousands of dollars in hardware and labor by 
switching to isolated containers.  The fact that they were full virtual 
machines likely made no difference at all.

>     I have to say, I think it's kind of funny that those of us running
>     low-power ARM devices as Myth MBEs are shunned for using "not real"
>     hardware and those of us using Atom / VDPAU for FEs are continually
>     warned of their "limitations" and are told to buy expensive
>     fire-breathing systems instead.

As has been explained multiple times, certain backend tasks such as the 
scheduler, are time critical.  Let them run too long, and you're going 
to suffer usability issues and lost recordings.  For small installations 
with one or two tuners and a handful of channels, an ARM or Atom would 
be plenty sufficient.  They will not have the power to commercial flag 
in a reasonable time frame, will be limited in the physical tuners and 
hard drives you can attach, and will not be powerful enough to handle 
several tuners and a large channel lineup.  Simply put, they are not 

MythTV is a hobby, and the funny thing about hobbies is that they tend 
to grow.  Users will add tuners, add more frontends, add hard drives, 
add larger cable lineups.  The ARM and Atom based backends do not have 
room to grow, and as such are a very bad recommendation to a new user 
feeling things out.  For experienced users with limited needs, they're 
fine... but then for experienced users with limited needs, they don't 
very well need to seek advice from a mailing list.

The recommended machines for frontends would be ones with sufficient CPU 
power to handle decoding whatever the user wants in software.  Hardware 
decoding is a nice bonus, but its capability is statically defined as 
what nVidia determined was 'good enough' several years ago.  It may not 
play your videos because you used encoding options or codecs they chose 
not to support.  It may not play your videos because of signal 
corruption.  You may find at some point in the future it does not meet 
your needs, and since it is defined statically and cannot be expanded, 
your only option is to fall back on software, or failing that because 
you bought an Atom, buy new hardware.  Again, for experienced users with 
known limited needs, they're fine... but it's a bad recommendation to a 
new user who doesn't understand the consequences.

While ARMs are a perfectly decent low power systems, MythTV doesn't 
support any hardware decoding options they offer.  Atoms on the other 
hand are simply garbage.  They offer similar performance to an ARM, at 
several times the power consumption of an ARM, and not all that much 
better consumption than more traditional hardware.  A homebrew ION 
system is going to cost somewhere around $250, and consume 15-20W when 
idle.  Pre-built systems will be over $300.  A mobile Core 2 (such as a 
Mac Mini) will be far more expensive, but will actually have lower power 
consumption than that ION.  On the opposite side of the spectrum, you 
can build a desktop i3 for around $300, that runs under 30W idle.  For a 
dedicated frontend, all you have to do is turn it off when not in use, 
and then most of the power consumption argument is moot anyway.

>     I'd say anyone running the recommended multi-core, multi-gig,
>     multi-spindle Myth system already has so much hardware overkill that
>     the tiny overhead of running a VM is a drop in the bucket.

Containerization is a perfectly valid and useful ability.  It makes 
system management much easier when you can isolate different servers, 
and prevent their upgrades from impacting other servers and applications 
on the same system.  Full system virtualization is not such a useful 
ability.  When you consider server farms often run distros like RHEL and 
CentOS which go for years without upgrading the kernel, the ability to 
run different kernels is not really that important.  How often do you 
really need to run both Linux and Windows servers on the same box, and 
is it really worth needing people trained to administer both systems of 
systems, rather than just more all servers to alternatives that run on 
one OS or the other?

Full system virtualization is good for two things, compatibility when 
you have no alternative, and for development and testing in a protected 
or cross-platform environment.  Virtualization took off because it 
intrinsically requires containerization, and so was what was available 
when administrators began to realize its usefulness.    Containerization 
is the desirable product, virtualization is just an unnecessary feature 
that came along for the ride.
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