[mythtv-users] Backend Hardware Questions

[Hika van den Hoven]

Hoi Hika,

Friday, January 16, 2015, 7:29:10 AM, you wrote:

> Hoi Mark,

> Friday, January 16, 2015, 6:00:51 AM, you wrote:

>> On 01/15/15 06:28 PM, Brian S wrote:
>>> Greetings all,
>>>
>>> Very Short Version: Do we think a Phenom II X4 B50 CPU stuck in a M4A87TD
>>> motherboard will have the ability to run well as a MBE & light-use desktop using
>>> an HVR-2250, 2 HDHR's, and 3 HDD's (OS on SSD)?
>>>
>>> Long Version: After running a rather computery mythtv setup for a few years, I'm
>>> attempting to downsize a little bit, and am wondering if converting my desktop
>>> into the only backend is feasible - it seems like it would be, but I have a
>>> knack for overlooking the obvious sometimes.
>>> Present setup is MBE w/HVR-2250 recording OTA + HDHR prime, SBE w/HVR-2250
>>> recording OTA (two antennas - I live halfway between Chicago & Milwaukee) and
>>> then a FE only.
>>>
>>> Was thinking I could move all BE's to an always-on desktop machine. Pertinent
>>> specs on the box in question:
>>> CPU Phenom II X4 B50 (4 core, 3.1Ghz)
>>> mobo Asus M4A87TD/USB3
>>> 8gb RAM (can bump to 16)
>>>
>>> So the general idea here is to pull the HDD's from the respective BE's and add
>>> them to the desktop computer, add one of the HVR-2250's to the desktop, and then
>>> replace the other BE recorder with another HDHR (due mostly to cabling issues).
>>> The OS runs on an SSD. The mobo has 6 sata slots so I should be ok with all the
>>> HDD's. (I realize I will also need to do other steps with fstab & database and
>>> what-have-you)
>>> The Big Question here is mostly just does the above machine have enough oomph to
>>> (theoretically but rather unlikely) record ~6 streams at once/run jobs/serve
>>> content to FE's while also being a desktop for mostly light-duty stuff? The only
>>> real CPU-intensive thing I can think I do is run virtualized windows XP for a
>>> few minutes at a time to scan documents to dropbox.
>>> And I suppose Big Question #2 is there anything I might be overlooking here that
>>> means this won't work or is a Bad idea?

>>   From a CPU perspectively, almost certainly.  I believe (not 100% familiar)
>> that all those recording devices either just provide the OTA mpeg data directly
>> to the system, or do actual mpeg encoding on the board.  So all the cpu has to
>> do in those cases is move the data from the encoding device to the hard drive.

>>   Likewise, when serving that data to the other front ends, it is just reading
>> the data off the disk and sending it over the network, which also requires very
>> little cpu.

>>   What will require cpu is if you do transcoding and commercial detection.  In
>> both cases, I'm pretty sure myth is good about not overloading the cpu, so it
>> may take a long time to perform those actions, but shouldn't affect normal
>> operation.

>>   I'm not sure the IO requirements for handling 6 potential streams at once.
>> OTA streaming can vary, but ~8 GB seems to be about worse case, which 
>> corresponds to about 2 MB/sec - actual performance of hard drives can vary, but
>> the IO pattern of myth is pretty friendly (sequential reads/writes), so that
>> shouldn't be much a problem.

>>   In the distant past, I used a system as both the backend, frontend, and a
>> linux desktop for my personal use (2 video cards - one for the FE, one for my
>> desktop).  That was with much older hardware (2005 timeframe), never had an
>> issue - I think I only had a single hard drive, but I also only had a single
>> tuner card.

>>   As a more recent comparison, my backend is pretty similar - think it may even
>> by the same motherboard, amd B95 quad core cpu, 4 GB memory, 3 OTA tuners, 9
>> hard drives.  In addition to the mythbackend task, I'm also running zoneminder
>> on it (7 capture devices, ranging from the composite on the ATI HDTV wonder,
>> pinnacle nstc PCI card I picked up cheap, 2 pinnacle usb adapters and 2
>> hauppauage hdpvr's).  And the zoneminder stuff by large takes up more of the
>> system resources, as the motion detection means the cpu actually has to do some
>> analysis.  And while the HDPVR's are nice devices (were $15 at local computer
>> surplus store), the fact that they provide an encoded mpeg stream means that the
>> system actually has to do more work to decode them for the motion analysis.
>> But with all that, the backend works just fine, and as I type this, 3 of the
>> cores have slowed down to 800 mhz (power saving) because there isn't anything
>> for them to do.

>>   I don't run an SSD in my system - if you already have one, great, but for a
>> system that is going to be on all the time, and ideally not rebooted very often,
>> I don't care very much if it takes an extra few minutes to boot up.


> Three things:

> - Add a second sata controller, where you spread the disks (where 0 is
>   OS and db, 1 is most used and 5 least) like:
>   0, 3, 4 on one controller
>   1, 2, 5 on the other
> - Check that your power supply can handle all those disk.
> - Don't use it for desktop things. Dedicate it as a server, possibly
>   even downgrading video to reduce power use.

One other thing: check your cooling, possibly adding a fan.



Tot mails,
  Hika                            mailto:hikavdh at gmail.com

"Zonder hoop kun je niet leven
Zonder leven is er geen hoop
Het eeuwige dilemma
Zeker als je hoop moet vernietigen om te kunnen overleven!"

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