[mythtv-users] RAID versus Drobo

[Eric Robinson]

Brian Wood wrote:
> 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".
>   

Ahh, gotcha!
>> 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.
>   
The first system I ever built was a SCSI U160 based drive (connected to
a Tekram controller in a standard PCI slot).  The drives I connected
were 10 and 15k rpm drives.  Speedy stuff: quite peppy!  Unfortunately,
SCSI remains a rather expensive technology: small, expensive drives
reserved for crazy server farms.  SATA is a lot nicer on the wallet and
can provide a happy boost in performance over PATA.
> I have heard of PCI-Express RAID cards, but I don't know anything about
> them.
>
> beww
>   
I've seen data on the PCI-Express based Areca 1200 series of RAID
cards.  They seem to scream.  Here's a review of the 1220:
http://www.xbitlabs.com/articles/storage/display/areca-arc1220.html
Spiffy, huh?

Eric