[mythtv-users] Some master/slave backend advise required

[James Bailey]

Hello 4GB is the minimum spec for ZFS then you should add more for MythTV,
I ran 16GB on my backend with ZFS on Linux and had no problems. You want to
limit your ARC to no more than 50% of RAM. If you are mainly writing SSDs
are not going to help unless you use a couple of smaller ones for the ZIL
because your ZIL is killing your IOPs. you need to mirror these because if
you lose a separate ZIL Drive your ZFS array is fscked. As always you
should pair ZFS with ECC RAM. don't bother with depude unless your workload
really suits it as it will kill disk performance.

If you haven't been there already talk to the people on the ZoL mailing
list they are very knowledgeable and quite friendly if you ask your
question right. You will get lots of tuning advise from them for your work
load.

If you end up splitting your storage from your backend, consider a couple
of cheap Infiband cards from Ebay crazy bandwidth 10Gbit ethernet emulation
or 20Gbit native.

Some of the new Intel Avonton storage boards are a reasonable price and you
can stick up to 32GB of ECC ram on them.

Jim


On 2 June 2014 19:59, Johan Van der Kolk <johan.vanderkolk at gmail.com> wrote:

> Hi,
>
> I’m running myth 0.27 (v0.27.1-7-g41d04b6) on Ubuntu server 14.04 with an
> i5(3GHz) and 4GB memory. I’m using 4 DVB-S2 tuners as source.
> Due to relocation of the dish I have to install a slave backend. I can’t
> (don’t want to) move my server to the garden shed.
>
> I have found that recording about 8-10 HD channels simultaneously will
> start killing processes on the backend (not the myth processes though), but
> the CPU load of the DVB-s2 stuff by itself requires 100% cpu.
> Mythcommflagging did not help either, although I could limit the
> simultaneous jobs to get more breathing space.
> So my thought was to solve both problems at the same time with a new slave
> backend, where the dvb-s2 stuff is running, by itself. Storage and
> commflagging still to be done on the master backend (which has 8TB of ZFS
> storage)
>
> I can see two issues now:
> Bandwidth: When recording 10 channels (what I want to achieve), I estimate
> worst case (based on what i recorded so far) 3GB per channel per hour, or
> 833Mb/s one way traffic, without other overhead. And not watching
> anything...
> How to solve this, and does myth traffic between master and slave benefit
> from Jumbo Frames. I could use two network cards in each machine, and
> create a 2 x1 Gb trunk between the switches.
> Second part of the problem might be that the ZFS file storage is not fast
> enough. (upgrade to SSD maybe)
>
> Configuration:
> Is it possible to configure mythtv in such a way that it does what I want,
> or are there better ways to do this?
>
> Any help appreciated!
>
> Johan
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