View Full Version : RAID Arrays & Video Issues

10-29-2003, 02:31 PM

Does anyone know where I could find a white paper or a more detailed explanation of the issues surrounding the use of IDE as apposed to SCSI drives for video capture and playback?

We have a Toaster system installed and realize that using SCSI drives are recommended (but without a hardware RAID controller). I was looking for more information on the technical reasons why the burst rate of fast IDE drives are problematic when trying to work with video and why it is that the SCSI technology is a better solution due to a "sustained data rate."

Paul Lara
10-29-2003, 03:22 PM
It's actually not an issue of 'burst', but instead of seek times.
Disk Speed (SCSI vs. IDE) is a measurement of how many megabytes per second your drive system can continuously pull from your drive array. A single uncompressed stream requires about 20Mb/s to be pulled from a drive for playback. When you build a RAID system, this allows all the drives in the array to act as if they where a single drive, dramatically boosting transfer rates, since the data is written across multiple drives.

Unfortunately, while the transfer rate from the drives is increased somewhat (it is not the combined speed of all your drives), the seek times are not. When you are playing back multiple streams of video on a system, the drive heads must seek in order to jump between the different files to pull the required frames. If seek times become too high, this will cause dropped frames since the drive head cannot reach the data fast enough (even though once it has been found it can be transferred very quickly.) Typically, SCSI drives have lower seek times, as well as higher transfer rates, and are therefore recommended for multiple stream-uncompressed playback.

Also important is the efficiency with which a drive system performs direct memory access (DMAs) across the PCI bus and into system memory. While impossible to quantify and gauge for a particular system without experimentation, it is generally found that IDE systems are less efficient than SCSI drives. However, there are users who have been getting very good performance from IDE systems. This does require more tweaking of your computer configuration.

Finally, there is the issue of mean-time between failure, or the expected life-span of the drive. SCSI drives typically ship with a 5-year warranty, while IDE the warranty period for IDE drives has just shortened from three years to one year.

Matt Drabick
10-29-2003, 03:26 PM
I don't know of any White paper to refer you to, but I can offer my opinion as a dealer that has built of lot of VT systems. Go with SCSI. You won't regret it, other than the price difference between IDE and SCSI drives. I think you will find that building an array with four Seagate Cheetah 36GB 10K drives is relatively affordable (under $800.00) and provides 2 hours of compressed or 10 hours of compressed DV video storage. Yes, building the same amount of video storage with IDE drives costs a lot less, but SCSI is the way to go.

With SCSI don't use a hardware RAID controller card. Those cards work in a burst mode, not a sustained data mode that video capture and playback requires. If you use such a card your video will stutter during playback. Simply use a standard SCSI controller (either a SCSI card or sCSI channels built into the motherboard) and stripe your SCSI drives into a RAID-0 using Windows. Very easy to do and it works!

I will get some argument on this but . . . IDE drives aren't as durable as SCSI drives for capturing and playing back video. IDE drives will wear out much faster than SCSI drives. Go with SCSI.
Better throughput (higher playback rates in megabytes per second for playing back multple clips of compressed and uncompressed video), better durability (5 year warranty versus 1, at best maybe 3 years, for IDE drives). etc.

Matt Drabick,
DigiTek Systems
Raleigh, NC

10-30-2003, 07:43 AM
Cool thread.

My next personal mobo will have SATA. It's my understanding that SATA will work it's way into very quick seeks and high-throughput over the course of five or six years after their intro. Apparently the manufacturers want to grow into the matured spec, rather than just jump in.

But anyhow, barring any warranty discussion, does what you've said mean that *perhaps* SATA will become an acceptable alternate to SCSI for VT?

My 2

Paul Lara
10-30-2003, 07:54 AM
Serial ATA drives certainly have improved seek rates. They seem to be pointing toward closing the gap.

Matt Drabick
10-30-2003, 08:05 AM
SATA looks promising, especially as the 8MB versions become larger in capacity, more plentiful and more affordable. Won't know about durability and reliability versus SCSI until a few years goes by, but it seems most SATA drives have a three-year warranty, which is a good indication of their reliability. One thought about any system you build . . . have a means of bacing-up projects. FireWire drives are large and very affordable, easy to swap out on your system, etc. Or simply add a very large internal IDE drive (say 200 or 300GB) as your back-up device for saving and/or archiving projects to.

Matt Drabick,
DigiTek Systems
Raleigh, NC

11-01-2003, 06:49 AM

Thank you for your excellent feed back on the RAID vs. IDE issues. What's really interesting about all of this is that although I supervise our live production program here in NYC, my main work is networking and systems administration.

Of course, we have been using SCSI drives for a long time, not only for our Toaster operation but also on our network servers. Recently, my associates have been experimenting with fast IDE drives as a replacement for some of their SCSI drives in some of their high demand servers. What they are seeing is that when there is a high load (many users hitting the same server for a single resource) the boxes installed with IDE drives can't seem to serve up the data fast eneough to keep up with the demand. So, although in the lab IDE drives appear to handle the load, when on a live network a desparity seems to exist between IDE and SCSI. None of the servers with SCSI drives fail when presented with the same user load.

Thanks again for the input. I will pass this on to both our network and T3 technicians.