[mythtv-users] Hard drive selection when Mythtv is in a VM

Thu Jan 4 14:09:48 UTC 2018

I'm running my mythtv backend in a VM on Fedora. I mirrored all of my VM
drives after having a failed drive last year. Having the ability to easily
snapshot a VM prior to making changes is invaluable. So is having the
ability to easily expand the drive to hold additional content, and easily
backup the VM by copying the qcow file to another drive.

One thing I'd do differently, and what others have mentioned, would be to
store the recordings directory on a separate VM drive. I could live with
losing my recordings, and it would keep the VM much smaller and easier to
back up. I will likely reconfigure this at some point.

-Lee

On Thu, Jan 4, 2018 at 7:23 AM, Jim Abernathy <jfabernathy at outlook.com>
wrote:

>
>
> On 01/03/2018 11:19 PM, Mark Wedel wrote:
> > On 01/03/2018 07:44 PM, Phill Edwards wrote:
> >>     I know some of you have Mythtv backends running in a VM. What is
> >> the best
> >>     way to configure the hard drive you use for recorded TV?  I did a
> >> test build
> >>     using VirtualBox 5.2.4 under Windows 10 and installed Xubuntu
> >> 16.04; just
> >>     used a partition on the VDI created for the VM for recordings.
> >> That works
> >>     in limited testing.  I think I could install a dedicated drive
> >> and configure
> >>     it just for the VM to use for recordings, but not sure that’s any
> >> better,
> >>     but it would be dedicated and not a dynamically created virtual
> >> drive.     Looking for what has been thoroughly tested.
> >>
> >>     I’ve also toyed with using the VirtualBox under NAS4Free.  I can
> >> just use a
> >>     directory on the NAS directly.  That VM has been very unstable
> >> so far
> >>     unrelated to the mythtv.  I’m chasing down potential problem with
> >> the
> >>     NAS4Free system to make sure it’s not hardware.
> >>
> >>
> >> I have a MythTV Backend running as a VM on Proxmox (Linux KVM-based),
> >> and have some CIFS shares on a QNAP physical NAS to store recordings.
> >> I like it that way because it makes backing up the VM easy as the VM
> >> isn't too massive (I'm not interested in backing up recordings). This
> >> has worked well for a few months now.
> >
> >  I can't say that I've tried using a VM with mythtv, but there are
> > some general notes:
> >
> > - If you just use a default image, this is usually represented as a
> > file from the host OS where virtualbox is running (in your case
> > windows) within the windows filesystem.  The Xubuntu then puts another
> > filesystem on top of that. This means that there are 2 filesystem
> > layers (Xubuntu + windows) that each read/write has to go through.
> > Generally, this is probably fairly minimal performance difference.
> > However, any optimization that Xubuntu tries to do may be lost.  For
> > example, in a normal case of writing to a hard disk, writing to a
> > contiguous sequence of blocks is probably going to be faster, because
> > there will be no seeking involved.  So Xubuntu may still do this, but
> > there is no guarantee that windows will write those blocks
> > contiguously - it might scatter those blocks physically over the disk,
> > depending on what blocks are available.
> >
> >  Note that if you are running on an SSD, seeks are no longer an
> > issue.  This presumes an actual hard disk.
> >
> > - If you use a network filesystem (nfs, share from a nas, etc), many
> > of these issues go away, since the protocol says 'write this file',
> > and the NAS can figure out best way to write it to disk. However, now
> > you are adding network latency, unless that share is from the same
> > physical host (eg, a share out from the windows to xubuntu means that
> > the traffic never leaves the box)
> >
> >  I used to run with NFS as the backend storage, and it seemed to work
> > reasonably well.
> >
> >  One advantage of using a share is that it unifies your storage
> > layout.  For example, if you have a 1 TB disk for windows and you want
> > xubuntu to store to use the virtual disk, you have to allocate some
> > amount of space, lets say 500 GB.  If down the road, you find out you
> > really only have 100 GB in recordings, but need another 200 GB for
> > windows storage, changing that layout is a bit of a task.  In
> > comparison, if you use network storage, perhaps you just give xubuntu
> > 50 GB (after all, you only need space for the OS).  Then, that
> > remaining 950 GB can be used by xubuntu or windows.
> >
> >
>
> Sounds like that is 2 votes for a small VM for Xubuntu running mythtv
> backend and  having the recordings streamed to a NAS somewhere else.
> Makes sense and easier to maintain.
>
> Thanks,
>
> Jim A
>
> >>
> >>
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> >>
> >
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>
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-- 
Lee Whitty
lee.whitty at gmail.com
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