[mythtv-users] Disk utilization on slave backend questions

Bruce Markey bjm at lvcm.com
Fri Jul 8 16:49:02 EDT 2005

Alex Brekken wrote:
> Hey all, I'm currently running a combo frontend/backend machine which
> has a 200 GB hard drive, and one PVR-250 tuner card.  I'd like to add
> a slave backend which would also have a PVR-250 tuner card and a 160
> GB drive.
> I feel like I have an OK understanding of how a distributed Myth
> system will work, but I'm a little confused about the best way to
> configure the drives.
> Does it make sense to put the 160 GB drive in the slave backend?  I


> assume that whatever recording is done on the slave, whether it's live
> TV or just a standard recording, will get written to that local drive.

They will be written to the directory on your prefix path set
in mythtv-setup. If that is a local disk, it will be written
locally. If the dir is on an NFS mount, the traffic will go
across the network,

>  So therefore, if the slave is down for any reason, then I obviously
> won't be able to watch whatever shows were recorded on it.

True. but if an NFS mount is unreachable during a recording, the
recording would fail. I'd rather grumble about having to fix a
machine before being able to watch a recording than to never have
the recording succeed in the first place. Network traffic can be
an issue but reliability is the main reason I use local disks on
my slaves. Another reason is that files are written contiguously
when there is only one being written to a filesystem rather than
fragmented with multiple recordings written to the same disk but
that's more something for Adrian Monk to worry about.
> Additionally, can the master backend/frontend machine just "see" the
> 160G drive on the slave?  Or do I need to set up an NFS or
> something...?

NFS or something. Myth doesn't know the fs type, it just writes
to a directory

> On the other hand, if I put the 160G drive on the combo
> frontend/backend box (along-side the 200G drive), then any recording
> the slave does has to be pushed across the network to the combo
> machine.  Is this a big deal?

Depends on the bitrate and network throughput. It will add some
latency but my not be noticeable. If you have any other apps that
saturate the net in bursts, you may get damaged recordings. These
would not be issues with local dedicated drives.

--  bjm

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