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

[Raymond Wagner]

> On Jun 2, 2014, at 14:59, 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.

Killing?  Are you OOMing?

> 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)

Running a significant amount of ZFS storage on a machine with only 4GB of memory is a mistake.  The ARC demands a better sacrifice.

> Second part of the problem might be that the ZFS file storage is not fast enough. (upgrade to SSD maybe)

ZFS is a volume manager, not just a file system.  You don't need to "upgrade" to an SSD, just add one.  Give each recording drive a ~1GB partition, defined as a ZIL.  ZFS will buffer writes to the ZIL, before committing them to disk.