Dual Hard Drives With Dual Tuners

[ArcticWhite]

Hi,

I have two 200GB SATA HD's in a two tuner PC I am building. I was wondering which configuration would be better for disk access throughput:


1. The two drives in a striped RAID configuration.

2. Have each drive on a separate disk controller and then assign storage from one tuner to one HD and storage for the other tuner to the other HD.

Basically, I want the best throughput to the disks, as I want to be able to record from both tuners at the same time in DVD quality, at the same time as either watching a recorded show or streaming a recorded show.

Thanks!

[merrypig]

A high quality video stream will be what, 12Mbps? lets say 2 Megabytes/sec to be generous. So recording two streams, and watching a stream, streaming a second is still 8 Megabytes a second.

ATA33 (slowest of the slow) can shift 33Megabytes per second via the interface.

Disk controller/interface will never be the bottle neck.

However. The random access time on the disk and time to read/write will matter, and SS doesn't appear to do anything special to mitigate this when running multiple tuners. Data is written as it appears so you can get constantly interleaved access between the two files. Depending on the disk fragmentation this could add a lot of head seeking between every write as it goes back n forth. This will start to drag down the thru put to /from the disk. Plus if you're playing back streams you'll see it impact even more.

If you have a striped raid configuration; you will get a performance benefit _IF_ the data access can be overlapped to each stripe. Depending on the organisation and efficiency of the raid contoller you might find that randomly accessing multiple files will simply mean that the consecutive data falls on the same stripe. You lose any performance increase of a raid controller in this situation (since it works by allowing you to access the other stripe while seeking on the other and so on ... masking the overhead. when you ahve to hit the same disk twice you can't hide the overhead).

However, if you use two disks; you can quite well manage the issue of storing seperate video streams in contiguous files. (that is if your recording pattern is such that you can assign jobs to alternate disks so that you don't end up recording two shows to the same disk at the same time...)

To be honest; yes there are particular configurations that will work for particular recording/usage patterns and give you the most optimal results.

If you were to ask me though; I'd just use two seperate drives. You don't need high speed interfaces/controllers - just need good file management. RAID doesn't really change that and is one more thing to go wrong.

For what it's worth, I have had a system running regular PATA 7200rpm seagate disks, recording two dvd quality shows and had no problem. Can't recall if I was watching at the time but I've never felt the system anywhere near it's limits to be concerned

[Xiadix]

I have recorded 2 shows and watched a show at the same time many times without any problems. Snapstream even did the Medusa using 6 input sources to one drive to show how much could be done.

I don't think we will have a problem until we get shhh...<looks around> HDTV ... Something that is still on my wishlist but not addressed by SS yet. Maybe for 4.0

KevG

[merrypig]

You know HDTV will come the moment that all of us have replaced 250's with 500's... And then we have to go replace em again with something else to capture hdtv instead

[flavius]

I knew there's got to be a reason not to replace my tuners. Thank very much.

[Rich A]

Originally Posted by Xiadix

I have recorded 2 shows and watched a show at the same time many times without any problems. Snapstream even did the Medusa using 6 input sources to one drive to show how much could be done.

I don't think we will have a problem until we get shhh...<looks around> HDTV ... Something that is still on my wishlist but not addressed by SS yet. Maybe for 4.0

KevG

I enjoyed the Super Bowl this weekend watching output from one of those ATI HDTV wonder cards. This was temporarily set up in a stand alone chassis as a dedicated HDTV PVR. (Until SS might hopefully add support for it)

CPU use during real time viewing was on average 10 to 15 percent. Quite low. However to obtain this low figure I set the default recording preset to "native". That enabled me to watch, pause, FF etc during real time viewing and still keep CPU use below 20 percent. The key is using "native" capture. What that does is simply "stream" the OTA digital signal as a transport mpeg directly to the hard drive without any encoding being done. I will say, the drive light was more active than normal. About 1 to 2 "blinks" per second. The result was 1920 x 1024 at an average of 18 Mb/s (peaks could be over 30 mb/s). The result was fantastic. Now IF I had opted to make the default something like MPEG-2 standard for DVD, it would have had to transcode the 1920x1024 down to 720x480, and this system uses a software encoder. Then you get up to the 80 percent CPU use. The playback of that rather large and fast streaming video was perfect, even though it was both saving to disk and reading during live viewing. The playback was also enhanced performance wise by using an ATI approved video card (a Radeon 9500 or better) The ATI environment used the firmware Directx 9 support built into the video card to also reduce CPU use.

All in all, the experience of watching the Super Bowl in high def projected to a six foot screen was astounding. The good news, IF you save in "native" mode there will be very little strain on the system. The only drawback being that you would have to later "transcode" that Mpeg-2 transport stream to something usable for DVD or what-ever.

Just for hoots, I used my Mpeg editor to cut out 2 minutes of the broadcast. Then transcoded that Mpeg-2 transport stream to an Mpeg-2 program stream. No modifications were used. So the resulting Mpeg-2 program stream was at full High Def. resolution and video bit rate. Dumped it to a disc and then played around trying to view it. It was nearly 400 mb large .. just over 2 minutes. Most players had difficulty reading it fast enough from a CD. However if I copied it off the CD to the PC's hard drive, I found Windows Media player (vers 9) played it just fine. It reported video bit rates from a low of 15 to a high of 25 mpb/s. Very impressive.

[merrypig]

Shame the Eagle's couldn't throw sharp though.