Using Raid 0 for Rendering?

[jaffacaique]

Hi, has anyone tried setting up raid 0 '2' drives for use when rendering / video editing? I have never used raid before and have read that it can be unreliable by some and yet stable by others. I was wondering whether I would still be able to use my existing HDD for all my usual stuff, i.e. OS, games, music etc without starting from fresh and just add '2' extra drives in raid 0 purely for video editing /rendering purposes without affecting my existing HDD.

From what I've been read everyone seems interested in using raid for their OS or Games!.

Any useful advice would be greatly appreciated.

[jagabo]

Unless you work with uncompressed video files a lot you won't notice any difference.

[fredfillis]

2 years ago I set up my PC with Raid 0/1 from scratch with the idea that Raid 1 would protect my OS partition and Raid 0 would give me a performance boost for video rendering. Using 2 drives with Intel Matrix Storage Manager. I'm using Vegas primarily.

These are the performance numbers I get from HD Tach. Not 100% sure this is telling me much about write performance with the "free" version of HD Tach.

RAID 1


RAID 0


I render out to the RAID 0 drive. Is it better / faster for rendering? I don't know given I've always run this configuration on this machine so I have no basis for comparison. The figures I see suggest it probably would be better but smarter people than me might be able to read more out of my HD Tach results than I can.

A final caution. With RAID 0 you double the chance of losing everything because a failure of either drive in the array will lose your data. Be sure you have a reliable backup methodology in place.

Cheers!

[jagabo]

If you are rendering standard definition video to MPEG for DVD you are writing about 1 MB/s to the drive. This is nothing to a single drive that can sustain more than 40 MB/s. So doubling the speed with Raid0 will not help.

Consider a fast CPU and MPEG encoder that can compress an hour long video in about 15 minutes. That will produce a 4 GB file. 4 GB takes only about 100 seconds to write to a hard drive at 40 MB/s. So in a worst case scenario the encoding might take an extra minute and a half. But keep in mind that write caching by the O/S will allow those writes to happen concurrently with the MPEG compression. So that minute and a half of writing to the drive is done at the same time the encoder is encoding and adds only a few seconds to the encoding time. You will barely save anything by using RAID1.

[redwudz]

I've ran RAID 0 in the past on PATA drives and lost all data on two occasions from a drive failure. I've also had the array fail ten or fifteen times, though that just takes a reset and no data was lost.

Newer drives and newer motherboard controllers are much more efficient than in the past. I just don't see as much a need for RAID 0 just for encoding most times. As jagabo mentioned, it does have applications for some types of material. But I would rather use that second drive for additional storage. I use three SATA drives on most of my newer systems, Boot, Edit and Archive. And I transfer or backup most data to a server over the LAN that has more space available.

You also have the option of a 15K RPM drive, which would likely run as fast as RAID 0 in real life applications. And the other RAID options are still viable, but you need more than two drives in the array if you want speed and data security. JMO.

[fredfillis]

I'm sure jagaboo is right in the situation described.

Maybe there is more advantage for more complicated situations, I don't know for sure without some comparisons.

For example.

I have avi from mini-dv tape / hi-8 captures and mpg2 from dvd-cam on the vegas timeline. With color corrections and transitions etc to render out to DV for writing to mini-dv tape for archive and later to mpg2 for DVD burning. Render times are measured in hours. With Vegas, I'm sending the "pre-render" avi's and all temporary files to my RAID 0 drive. My guess is this is quicker with RAID 0.

[edDV]

I'm sure jagaboo is right in the situation described.

Maybe there is more advantage for more complicated situations, I don't know for sure without some comparisons.

For example.

I have avi from mini-dv tape / hi-8 captures and mpg2 from dvd-cam on the vegas timeline. With color corrections and transitions etc to render out to DV for writing to mini-dv tape for archive and later to mpg2 for DVD burning. Render times are measured in hours. With Vegas, I'm sending the "pre-render" avi's and all temporary files to my RAID 0 drive. My guess is this is quicker with RAID 0.

All of that is delayed by the CPU not the disk system so RAID 0 won't help. DV format writes are less than 4MB/s.

RAID 0 is needed for uncompressed editing with "real time" hardware cards where multiple uncompressed streams are being input (e.g. A roll, B roll and alpha) and a realtime stream is output for encode. For SD SDI (SMPTE 259M ) sources this means the disk system needs to handle simultaneous 4x270Mb/s = 1080Mb/s or 135MB/s sustained data with random access. This in theory might work with a 2 disk SATA raid but seek time kills that idea if any fragmentation exists. It usually takes a 4-8 disk RAID 0 for reliability. This requires a special hardware RAID controller, not the software controllers used on mother boards.

Another example is working with single uncompressed* HD feeds (e.g. from Black Magic Intensity or Decklink). A single uncompressed 720p/59.94 feed requires 848 Mb/s (106MB/s) so is on the edge for a single Raptor 10,000 RPM drive, so would typically need a 2 disk RAID 0 for capture. 1080i/29.97 at 960 Mb/s (120MB/s) always needs a 2+disk Raid0 for uncompressed capture.

A realtime hardware HD setup with A/B/alpha rolls to record would take a minimal 8 disk RAID (no fragmentation) but 10-12 disk would be more reliable.

Back to the home user, single uncompressed 720x480 4:2:2 feeds (like from a BT capture card) are ~ 180 Mb/s (22MB/s) which is within sustained range of a current ATA133/SATA 150 drive. In the past with slower drives, instead of RAID, most used lossless compression software like Huffyuv to use CPU load to reduce bit rate to ~ 48Mb/s (6MB/s) that can be easily handled by a single ATA66/SCSI 3 drive.


* Most home users are working with compressed HD files in the 8-25Mb/s (1-4MB/s) range so standard PATA/SATA drives are more than adequate. The load all goes to the CPU and hardware decoding display card.

PS: HD realtime RAID arrays are usually externally mounted and connected by multiple SMPTE-292M feeds to the realtime card in the PC. For example ...


http://www.dvsgroup.com/Products/Broadcast/HiDEF_CreationSTATION_Pro/

[jagabo]

Think of video encoding like a simple two person assembly line:

One person (the CPU) packs widgets into a box. The second person (the hard drive) takes the boxes off the line and stacks them in the next room.

It take the first person 100 seconds to pack each box. The second person takes 10 seconds to pick the box up, move it to the next room, and return. But the first person doesn't wait for the second person to return before starting on the next box. So 100 boxes takes 10,000 seconds (100 * 100) plus the time to move the last box from the assembly line to the next room, a total of 10010 seconds.

Adding a second person to move boxes to the next room (setting up a raid 0 array) doubles how fast you can move boxes. But the bottleneck is the guy packing the boxes. The two guys moving the boxes will stand around doing nothing most of the time.

If the times are switched, it takes 10 seconds to pack a box and 100 seconds to move it, then it makes sense to hire a second guy to move the boxes. This can happen with uncompressed video when you are moving lots of data around and not processing it much.