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

[belcampo]

jedi wrote:
> 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. 
I can copy a 1398376250bytes file from my network to local disk in 
23.01sec, so 60772544bytes per sec. but lots of small-files is a totally 
different story because of seeking. And that is what 
recording/flagging/watching of 4-.. files at a time is all about.
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.
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