[mythtv-users] Running mythbackend on a low-power device

[tortise]

On 1/12/2012 12:24 a.m., Mark Small wrote:
> On Thursday 29 November 2012 20:33:47 Tortise wrote:
>>
>> I've been considering using a Rpi master backend, that connects with a
>> hdhomerun (or two?) and some sort of inevitably noisy multi hdd multi TB
>> machine out of ear shot in a utility space, preferably with demand power
>> control on that machine.

{Deletia}
>
> I'm not sure that I'd like to have my storage on a machine that that powers on
> on-demand.  Does anyone do this? I'd worry about lag on viewing.  Does myth
> know how to wake storage on demand?
>
> You might need to have your storage box on all the time.   If storage is on a
> machine that is on all the time, might as well just run the backend on the
> storage machine.

I agree that is a concern.

I was mindful that backends can be made to save power by turning off 
when there is no activity / recording scheduled.

see http://www.mythtv.org/docs/mythtv-HOWTO-11.html

However I am yet to fully understand what happens when a user turns on a 
frontend and seeks to view a recording / live TV when the backend is 
suspended / off?

http://www.mythtv.org/wiki/User_Manual:Detailed_configuration_Frontend 
details the checkbox "Enable Database Server Wakeup"

http://www.mythtv.org/wiki/ACPI_Wakeup

It seems the frontend (logically) will trigger the backend to WOL, but 
using ACPI, which seems independent of WOL?

My backend gives:

mythtv0:~$ grep -i rtc /var/log/kern.log
mythtv0:~$ grep -i rtc /var/log/messages

however also:

mythtv0:~$ cat /proc/driver/rtc
rtc_time        : 10:34:37
rtc_date        : 2012-12-02
alrm_time       : 08:08:21
alrm_date       : ****-**-**
alarm_IRQ       : no
alrm_pending    : no
24hr            : yes
periodic_IRQ    : no
update_IRQ      : no
HPET_emulated   : yes
DST_enable      : no
periodic_freq   : 1024
batt_status     : okay

Which I assume means it has the capability.  (Gigabyte GA-EP41-UD3L)

I've been toying with the idea of having a low power master backend with 
a higher powered server however given the constraint of also wanting to 
be able to record up to (say) 8 HD streams simultaneously (all be it 
uncommonly)

If anything is recorded then the bank of HDD's need to be on, whether 
they be on a NAS or some other machine.

It seems the best and simplest thing to do is to run one powerful power 
hungry backend and just turn it off whenever one can!  Seems the price 
of the power saving is a user start delay while the backend resumes...?

Have I set this out correctly?  Can anyone tell us how well the end user 
Frontend wakeup of a backend works and how much longer users wait in 
practice (when the backend is awakened from supend)?

The other thing I'm not sure about is the auto runs of mythfilldatabase, 
will the backend turn on to run this as scheduled and suspend again at 
the end of the run?