[mythtv-users] MythTV Installer Usability: An Analysis

Rudy Zijlstra mythtv at edsons.demon.nl
Fri Nov 4 05:17:45 EST 2005

f-myth-users at media.mit.edu wrote:

>	Date: Fri, 04 Nov 2005 18:32:51 +1000
>	From: ffrr <ffrr at tpg.com.au>
>	Is this because the ringbuffer file seems to continually grow?  I have 
>	noticed this.  Why does it do that? If you are not paused, surely the 
>	file size should remain stable?
>    Yes.  The ringbuffer grows monotonically -up to its configured limit-
>    and then (I assume!) stops growing.  It's not clear to me why the
>    installer defaults to a partition sufficient to hold 5.3 hours' worth
>    for a 200GB disk, though; that seems like an awfully large buffer.
>Hmm.  It belatedly occurs to me, of course, that the installer has no
>way of knowing at the time it's partitioning the disk whether you're
>planning on putting an HD card into the machine, either now or
>sometime in the distant future, and an HD card might require quite
>a bit of disk space to have even a moderate-duration buffer.
>(This also makes the time-to-explode far shorter in this case.)
>What -really- doesn't make sense to me, though, is why this thing
>is in its own partition to start with.  Why not just put it in the
>same partition that holds recordings?  Then it could trivially be
>as large as the freespace on the disk, while not actually soaking
>up space used for recordings if you'd rather use the space that
>way (e.g., just dynamically adjust the ringbuffer to never exceed
>the freespace on the device, plus maybe a margin so it can shrink
>over time if the rest of the partition is filling up with recordings
>from other tuners).  The current situation just wastes a lot of disk
>space in order to be less flexible and more buggy.  (Is this specific
>to KnoppMyth?  Having not (yet) rolled my own installation from a
>different distro, it's difficult for me to tell.)
>This is especially acute if one is setting up an MBE/SBE system,
>as I am.  It's not clear to me at all how many ringbuffer partitions
>there need to be---one for -each- machine in which some capture card
>might be looking at live TV?  It's tempting to make only one, and
>share it via NFS, but maybe I can live with one per machine just to
>make the configuration easier and more robust.  I've also seen the
>installer pick both 12GB and 5GB sizes for that buffer, and I have
>no idea under what circumstances it decides; after so many reinstalls
>in the past week, my memory on this is a bit hazy.
Hmm, this is a case where i actually agree with the knoppmyth installer. 
I have several tuners (6 total) and when 5 (current concurrent max) are 
recording at the same time, i do not want the IO from the live buffer on 
the same disk-set. Also, for demo purposes i sometimes watch the demo HD 
MPEG2 channel, this takes a lot of data to the live buffer. For this 
reason the live buffer (actually all of them on the same) are on a 
separate U320 SCSI disk, used only for this. (bit of over-capacity, but 
i hate failures).



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