[mythtv-users] How much ring buffer is too much?

[Michael T. Dean]

On 03/20/2008 12:09 PM, Richard Shaw wrote:
> I ordered a new 500GB hard drive (Segate SATA 3G w/ 32MB cache) just
> to store media on my FE/BE system. I'm thinking I'm going to allocate
> about 10% of the space to the ring buffer. Since one of my ATSC HD
> recordings took up just over 6GB for one hour that should give me
> about 8 hours of buffer worst case.
>
> Are there any downsides I should be aware of? Will this put a
> significantly increased load on the database? I currently have a
> marginal HD playback system and have to use the Slim playback profile
> to get good 1080i playback. Of course the original 250GB drive is
> staying in the system.

For quite some time, now (since 0.18?), there really hasn't been any 
allocating "space to the ring buffer."  In 0.21, there's an ability to 
create a storage group specifically for LiveTV (with the specially-named 
LiveTV storage group).  This is really meant to be used to allow writing 
LiveTV to local storage to prevent a round trip to an NFS/CIFS server or 
for writing to "fast" storage (i.e. if you have your recordings going to 
a RAID array, but you don't want to waste the effort RAID'ing your LiveTV).

However, using the storage group to keep from auto-expiring other shows 
doesn't really make much sense.  If you set aside 50GB of the disk for 
LiveTV, only, that means that you always have 50GB less space available 
for recordings--even when you're not using LiveTV.

Also, LiveTV is /always/ expired at higher priority than recorded shows, 
and new LiveTV files are created at every program change (assuming you 
have guide data) or on the hour and the half hour if you don't have 
guide data.  Even if you have guide data that contains "extra long" 
programs, there will be an artificial break inserted at 8 hours, meaning 
at that point, a new LiveTV file is created and the 8 hour one (taking 
about 50GB by your calculations) would be expired, so you won't lose any 
more recordings to auto-expiration than you would have lost anyway 
because of the space you didn't allow for recordings.

And, if you use the Watched Flag appropriately, you can ensure that 
after LiveTV recordings, shows you have already watched are expired 
next.  http://www.gossamer-threads.com/lists/mythtv/users/321904#321904

Mike