[mythtv-users] RAID versus Drobo

Brian Wood beww at beww.org
Mon Sep 10 20:05:56 UTC 2007

Eric Robinson wrote:
> Brian Wood wrote:
>> Eric Robinson wrote:
>>>> Have a look at this:
>>>> http://library.creativecow.net/articles/gerard_rick/premiere-pro-HD.php
>>>> Of course if you plan to record one stream while watching another,
>>>> record multiple streams, or do anything else requiring disk I/O at the
>>>> same time you'll want more than that chart implies.
>>> Umm... If you're pointing to the graph on that page then it's a little
>>> different.  That's completely Raw HD.  Nothing in MythTV is done in
>>> Raw.  My understanding is that it's Mpeg2 generally and can be converted
>>> using Mythtranscode to some version of mpeg4.  In any event, I figure
>>> MythTV buffers a certain portion of the video on the frontend before
>>> beginning to play in case of heavy network jitter.  One hour of 1080p
>>> content is 7GB or so, right?  I feel like I read that somewhere in the
>>> docs...  Anyone have any success stories with playing back HD content
>>> and with what drive interface speed?
>> Ooops, right you are. I confused your thread with another from another
>> group and sent you the wrong link.
>> You might look at:
>> http://broadcastengineering.com/news/broadcasting_psip_data_broadcasting/
>> (though it's a bit dry and obscure), or:
>> http://en.wikipedia.org/wiki/ATSC_Standards
>> Basically the full G3 data rate for an ATSC transport stream is 19.4
>> Mbps, so if your storage system can handle that you should have no
>> problems with a single stream, even if it's using the full available
>> bandwidth (which most don't).
>> I've had no problems playing back HD (as the original MPEG2 or MPEG4
>> (H264-2)) from a single PATA or SATA drive. I haven' tried multiple
>> streams but from the specs it should work for 2 or even 3 streams
>> without trouble.
> Ahh, good stuff!  The Wiki link you sent has this for the actual quote,
> though:
> "Terrestrial (local) broadcasters use 8-VSB modulation that can transfer
> at a maximum rate of 19.39 Mbit/s, sufficient to carry several video and
> audio programs and metadata."
> I may be misinterpreting an ambiguous sentence but that sounds like
> 19.39 Mbit/s is for multiple channels?  Or by "programs" do they mean
> streams (as in one video with multiple language tracks)...?

They can send multiple videos. That speed is the "transport stream",
which can contain one or more "program streams".

> Either way, I think I'm fine with software SATA RAID-5...

Agreed, totally.

With PC hardware you're not going to get anything faster than ATA in
either the P or S incarnation. You'd have to go to SCSI drives, and even
then most consumer mobos have only 32-bit PCI slots and most U320 cards
want a 64-bit controller, as do most hardware RAID5 cards.

I have heard of PCI-Express RAID cards, but I don't know anything about


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