[mythtv-users] Backend for fast commercial flagging (HD-PVR recordings)

[jedi]

On Tue, Mar 24, 2009 at 05:48:04AM -0700, Steve Heistand wrote:
> Ronald Frazier <ron at ronfrazier.net>, said on Tue Mar 24, 2009 [08:20:33 AM]:
> } >>> I will be doing up to 4 commercial flagging jobs at once, depending on
> } >>> what's on of course.
> } >
> } > Won't you run into disk-i/o troubles, stuttering ..
> } 
> } He was asking about 13Mbit files, so if he needs 4 recording + 4
> } flagging  (not to mention anyone watching a recording) then he's gonna
> } need 104 Mbit/sec. Even the fastest hard disk (the velociraptor) won't
> } keep up with this (even it's sequential read/write speeds will drop
> } below this from time to time). However, any pair of half decent hard
> } drives should have no trouble handling this as long as the recordings
> } are split between them, or if they are in a RAID 0 setup.
> } 
> 
> your average sata drive is 30-40 MB/s, really good ones 70MB/s.
> but fortunately 104 is Mbits not MB. so a single drive could keep
> up with 4 streams. though if its also a system drive it wont
> be happy about it.

     Something else to consider is frontend performance while all of this 
is going on. You might be able to record off of 4 tuners, and flag it all
concurrently but you might find your frontends unusable. In my own setup,
I have my jobs shut down right before "prime time" because I sometimes
see performance issues with recording off of my 4 tuners and running jobs
at the same time while watching stuff. At a certain point, the master
backend starts to get bogged down with all the IO (network/disk) associated
with all the jobs and recordings.

      It's not just the aggregate bandwidth but managing all the different
processes driving it and juggling the concurrency.