[mythtv-users] Backend Hardware Questions

[Stephen Worthington]

On Thu, 15 Jan 2015 20:28:37 -0600, you 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?

My MythTV box (combined front- and backend) is:

Asus M5A97EVO motherboard
AMD FX-4100 Quad-Core (3.6 GHz)
8 Gibytes RAM
3 x DVB-T tuners
2 x DVB-S tuners
7 recording drives (one also has OS on it)
3 videos drives
500 W power supply

My case is only big enough for three drives internally - the rest are
hanging off the back of the case on internal cables pulled out through
an empty slot, except for the videos drives and one recording drive
that are in a four drive mount with its own fan and power supply and
connected via port multiplier to one internal SATA port.

My OS+recording drive is a fast one (Hitachi HDS723030ALA640).  That
is important as the peak load of the mythconverg database activity can
be very high.  I have five multi-rec virtual tuners per physical
tuner.  The DVB-S tuners normally record no more than three programs
at once between them, plus overlaps.  The DVB-T ones can be recording
two each at times, plus overlaps.  So it can be recording as many as
14-15 programs at once.  That only works out to two per disk usually -
that seems to be the limiting factor.  Three per disk should be OK,
but four is pushing it, especially if you also want to be able to do
playback at the same time.  I do commercial flagging also, but most of
the time that does not cause any extra disk load as the CPU is fast
enough that runs in real time using less than one core per program. So
as it is real time, it can use the data directly from the RAM buffers
rather than having to re-read it from disk.  I have it set to do only
four commflag tasks at once (one per CPU core) so that it will be able
to run like that.

The really important thing is that all my tuners require only that the
CPU just writes the data streams received directly to disk with no
encoding.  If encoding is required, it completely changes things.
Playback similarly does not involve much CPU as my Nvidia card does
the decoding.

I have had no problems using the PC to compile things at the same
time, although I do not think I have done any compiles at the same
time as a maximum recording load.  The box is also a DNS and NTP
server, runs my OpenVPN encrypted connections when I am away from
home, records the netflow data from my network to a database and
probably half a dozen other little jobs I have forgotten about.  There
always seems to be plenty of CPU and RAM left.

So I would say that your system should be able to cope with what you
want it to do.  If you want to run a serious virtual PC, then more RAM
is normally what you need for that, as any RAM assigned to the virtual
PC tends to be fully devoted to that purpose and should be subtracted
from the RAM available for general use.

With that many drives in close proximity in one case, you will need a
fan that moves air directly across the drives to keep them all cool
enough.