RAID and the Ideal External Media Drive

For many people, editing video using your internal hard drive as a scratch disk (where you store your audio/video material) is a fine choice. But what happens when you begin to edit multiple layers of video and include stacked filters, motion effects and composites? Your ability to handle real-time playback will decrease because there are more rendering tasks your computer has to handle in order to play your sequence without rendering. You’re thinking “I have a a fast computer with multiple cores.” Processing capacity reflects your computer’s ability to render, because rendering is the process of calculating many complex mathematical equations to create new rendered video as the result. But we’re trying to increase our computer’s ability to handle more tracks, more effects and more complex sequences without having to render. This is real-time playback ability and is very dependent on how fast your computer can read your video material from your hard drive. When your video is on your internal hard drive, your computer is reading data for your operating system, open applications and your video all from the same source. This can cause congestion. By putting all your project data, video and audio material onto a high performance external hard drive, you are relieving your computer’s internal hard drive of performing double duty.

So the answer to increasing the performance of your video editing/animation/graphics workstation is to go out and buy an external hard drive. Stop right there! Not all external hard drives were designed for video editing. Most of them were intended for file backup or photo and music storage. You need a high performance external storage system designed for the much higher demanding tasks of multi-track video playback and rendering. So what makes an external hard drive suitable for video editing?
Factors

Read Speed and RPM’s

This will depend on what type of video you will be working with: compressed (MiniDV, HDV, DVCPROHD, XDCAM, etc..) or uncompressed formats. The faster the read speed, the more complex layers you will be able to playback in real-time. Compressed formats require less speed than uncompressed formats. Your typical internal hard drive has a read speed of 35-45MB/s. External RAID 0 hard drive solutions (containing two hard drives) can over 80MB/s. Solutions with even more hard drives can achieve speeds far beyond that. A hard drive’s speed can be gauged by the RPM rating such as 7200rpm or 5400rpm. Most people know RPM stands for Rotations Per Minute, but no all are clear on what it means for hard drives. On the inside of a hard drive lies a disc that spins. The fast it can spin, the faster data can be transferred. Typically, internal desktop hard drives run at 7200prm while most laptop hard drives run at 5400rpm. There are some higher end laptop models that have 7200rpm hard drives, but manufacturers typically use the slower drives because they require less energy and therefore extend battery life. For media applications look only at drives that are 7200rpm or 10,000rpm (enterprise class) drives.

Average Latency

Latency is a time delay between the moment something is initiated and the moment its first effect begins. Think of it as reaction time and the lower the number the better. Figures of 4.2ms and under are suitable.

Average Seek Time

For data to be read or written, the head in your hard drive needs to be physically moved to the correct place. This process is known as seeking, and the time it takes for the head to move to the right place is theseek time. As with latency, you want a lower number for seek time. Figures of 8.5ms and under are suitable.

Heat and Air Flow

Excessive heat spells certain death for hard drives. You want a media drive that has a suitable fan and ventilation to expel heat. Fans tend to increase the amount of noise pollution, but low rpm fans have shown to provide an excellent balance of cooling and sound pollution. Aluminum casing also works well at dissipating heat from the hard drives.

RAID Controller

You want to stick with a hardware controlled RAID system, not software based. This means dedicated hardware is controlling the data being read and written between the two hard drives.

Data Cache

Hard drives with larger caches perform better under heavy loads. For most applications, a moderate cache of 8MB is fine. But for video editing, hard drives with 16MB-32MB cache (each) is very necessary.

Hard Drive Reliability Rating

The rating system used is called MTBF, or Mean Time Between Failures. This measures the useful life of a hard drive by the amount of hours it is expected to run before it starts dying. Figures of 1 million and above are suitable.

Hard Drive Interface

You may have heard of terms such as IDE/ATA and SATA. Those all refer to the interface your hard drive uses and to connect to your hardware RAID controller. SATA provides internal speeds of up to 3GB/s while IDE/ATA drives max out at 100MB/s. The difference is huge but the price is not, so stick with SATA drives.

Computer Interface

Most likely your internal hard drive is connected to your motherboard with a SATA interface. So why buy a USB 2.0 based external hard drive? The way you connect your external hard drive to your computer is very important. There are USB 2.0 drives with a maximum data transfer rate of 480Mb/s and then there’s Firewire 800 with a maximum data transfer rate of 800Mb/s. If your computer supports Firewire 800, use it instead of USB. Slightly more expensive external RAID drives now offer eSATA interfaces which bring the speed up to multiple Gb/s.

RAID 0 Explained

Hard drive performance is very important when editing multiple tracks of video with motion graphics, effects and composites. Real-time playback ability is dependent on several factors, one of the most important ones being the speed your hard drive can read data. RAID 0 is a method of stripping two hard drives together allowing them to share the workload evenly. Blocks of data alternate between the two hard drives increasing performance beyond the capabilities of a single hard drive. Another advantage of RAID 0 is that multiple hard drives will appear as a single massive drive on your desktop, simplifying media management. RAID 0 can be achieved through hardware and software means. The software approach is inferior because of added stress to your processor. Having RAID 0 handled by external hardware relieves that stress and increased overall performance.

The Balance of RAID 0

RAID 0 provides increased performance, but comes at the cost of reliability. Essentially, in RAID 0 half of your data is stored on drive one and the other half on drive two. In order to piece together your data, blocks from both drive one and drive two need to be intact. If one of your drives fails you lose all of your data because it cannot be reassembled from just half the information. Fortunately, modern high quality hard drives have a very low failure rate. They also warn you as they are dying by clicking and beeping. When you hear that, transfer your important data off the drives. The balance of RAID 0 means you sacrifice reliability for performance. But since hard drives have become very reliable, the sacrifice is worth the net gain in performance especially since RAID 0 is the cheapest way to get this level of performance. If you are working with compressed formats such as MiniDV, HDV, DVCPROHD or XDCAM, a two-drive RAID 0 external hard drive solution will work very well for you as long as you connect it to your computer with Firewire 800. If you are working with formats such as uncompressed, HDCAM or other very high bitrate formats, a RAID 5 solution connected to your computer with SATA would be ideal.

RAID 5

RAID 5 allows you to have the performance benefits of RAID 0 without compromising reliability. Instead of striping two hard drives together (as in RAID 0), RAID 5 typically involves four or more hard drives. In short, RAID 5 spreads data across more drives allow for increased speed while also providing redundancy by replicating data across multiple drives. This means that you will lose some of your capacity to this practice of parity. In a four drive RAID 5 solution, your total capacity will be the sum of three of your drives. For example, if you configured a RAID 5 with four 1TB drives, instead of having a capacity of 4TB, you will have a total capacity of 3TB. You sacrifice space for increased performance and reliability over RAID 0. RAID 5 is more expensive than RAID 0 because it requires more hard drives and a more costly hardware RAID controller.

So What is Best for Me?

It really depends on what format of video you are working in, your budget and the overall scale of your projects. Post-production workflows for corporate, web video projects will be different from national television series and feature film workflows. For most small production environments, independents, students or teachers, RAID 0 fits the bill nicely. For larger production environments where clients are present and the need for real-time playback of detailed graphics, animation and multiple tracks of HD video is necessary, RAID 5 would be more suitable.

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