[mythtv-users] Build for dual HD recordings - also is PSU enough/too much

[R. G. Newbury]

On 03/14/2011 03:03 PM, Digital Hit Entertainment wrote:
>
>
>> You need to consider the worst case situation of recording 2 HD shows concurrently, during playback of another HD show while maybe also doing advert detection/transcoding in the background and remaining responsive to other activity such as input from a remote and/or slave frontends.
>> One harddrive isn't going to cut it. It will definately be the bottleneck.
>> My Mythbox has 3 HDs (not raided):
>> The system and mythtv apps on an old/fairly slow 100GB HD. A fast 1TB HD for TV recordings only, and a 3TB v.large but slow (green) HD for static media like ripped DVDs/Blu-rays and music.
>> Several people have said here that you need a fast drive for your OS drive. I totally disagree as other than at bootup, its really not doing much if your recordings are going to another drive.
>>
>> If you buy just one more drive, make sure its fast and use it for the TV recordings only. thats the drive that has to deal with high-bandwidth I/O over a long duration especially if you're recording multiple HD streams while potentially playing back another.
>
> Interesting point.
>
> I actually don't have much of a DVD collection, so if I'm splitting to two drives, my storage drive would most likely just be recorded TV shows. So that should be a fast drive too then?
>
> Or am I missing something in the "workflow" of MythTV? Or when people talk about static media drives are they talking mostly ripped DVDs and music. That probably won't be my immediate usage. Just wondering if I should ditch the green 1.5 TB for a faster one.

There are 2 different considerations here: If you are recording multiple 
shows, and perhaps also watching one of those shows, the bottleneck 
(such as it is) is the disk and controller for where those shows reside.
Realistically, there is no such bottleneck for these types of streams.
I have a number of times had 3 HD streams (all OTA) and one SD stream 
(digitized cable feed using PVR-500)  being recorded AT THE SAME TIME I 
WAS WATCHING another show.

Meanwhile, the OTHER bottleneck, is commflagging and the database. This 
is all mysql table entries and while that is going on, you might also be 
commercial skipping in the show you are watching.
This is a different sort of bottleneck, but it does depend on quick hard 
drive access.

I disagree that a 'fast' video store disk needs to be preferred over a 
'fast' OS disk. The usual stuff (SATA) seems to work quite well as a 
video storage disk. But I definitely noted it when I ran my mythbox from 
a USB key for a day or two...that was SLOW! I was very happy to get the 
new install completed.

Note that arguing about the necessary disk *speed* is quite distinct to 
the arguments about splitting up where your various partitions are 
actually stored.

Geoff


-- 
              R. Geoffrey Newbury