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

[Jim Abernathy]

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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