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09/05/2006
Striped RAIDs
Ever since we've been building video-editing workstations, we've tried to get as much performance as possible out of the systems. One of the biggest bottle necks is hard drive speed, although for many people this is no longer the case. Because of the demanding throughput needed when editing video, RAIDs became synonomous with Video Storage and, particularly the RAID 0.
RAID 0 or Striped RAID is a method of taking multiple disks and interleaving the data across each drive evenly. During reading and writing tasks each member disk can give or take data at its maximum rate. This means that the total read/write rate will be improved for the RAID group when compared to a single drive. The increase in throughput will be about equal to 75% of the sum of each member drive's throughput. There is some overhead from the CPU or RAID controller depending on how the RAID is constructed, but the more drives you have the faster throughput you will get. Once the drives are "striped" together you will only see one logical drive inside of Windows.
Deciding how many drives you need in your RAID, or if you need a RAID at all is as easy as determining what type of video you are going to edit and how many simultaneous streams of video you need. For example, our standard RAID for the AXIO LE systems is a RAID with 15 SATA2 drives. This will allow playback of three uncompressed 8-bit HD video layers. Our standard DV/HDV RAIDs are comprised of 2 SATA2 drives and will allow simultaneous playback of 10-15 layers of video. A single SATA2 drive can give the DV editor about five simultaneous video streams of playback.
The Dark Side
There are two bad reasons to have a RAID 0 that I can think of. One is more philosophical and one is more technical, but they both have to do with hard drive failure. First, the technical reason: If one drive in the RAID 0 fails, then all of your data will be lost. Since the data is spread evenly across each member drive losing even just one drive out of 15 means all the data is gone. Data recovery is sometimes possible but can be very expensive.
It should be understood that the main reason to have a RAID 0 is to increase the performance of your video storage. I recommend choosing the right size of a RAID based on your typical project size with enough room to expand. You should not use a RAID 0 for project archival. To keep your RAID 0 operating at maximum performance you should defrag it periodically, or even better, format it before you start each new project. You should not keep your only copy of important footage, pictures, or documents on a RAID 0. Yes, I know that big hard drives are cheap now, but if you want to archive everything consider a different storage solution that offers data protection like RAID 5 (Which I'll talk about later).
It is always sad to have to inform one of our customers that because one of their drives went out on their RAID, all their data is gone. Hopefully, you can understand a little better now the purpose of the Striped RAID.
Ashley Guy
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