A RAID, which stands for Redundant Array of Inexpensive Disks, is a set of connected hard drives that is designed to store information in a more reliable manner.
As the size of RAW files increase (5D Mark III full RAWs are approximately 27MB for example), many professional digital photographers and videographers depend on RAID systems. Professional digital artists make use of the large storage space for their digital RAW photos and uncut video in the event that they need to refer back to them at a later date. RAID systems are also used as a reliable system to back up content within its multiple drives. As stated in the SSD vs. HDD article, all drives fail. It isn’t a matter of IF, but WHEN. RAID systems have the ability to copy and redistribute data across the set of connected hard drives making data recovery of a failed drive seamless.
Raid storage technology combines multiple large capacity disk drive components into a logical unit with fast data access. Most current systems offer capacities from 2 to 8TB, and are compatible with Apple's MacBook Pro, Mac Pro, G5 and G4 computers, as well as Linux and Windows workstations.
There are several different levels at which a RAID system can be configured. In the photo and video industry, we generally use RAID levels 0, 1, 5, and 6. One way to remember them is: Fastest (0), Mirror (1), Safe (5), and Safest (6).
A RAID 0 (also known as striping) provides maximum performance and speed by accessing multiple drives simultaneously.
RAID 0 does not provide any data redundancy, which is a high risk, but offers the fastest speed of all of the levels by breaking up the data into smaller blocks and then writing a block to each drive in the array.
The probability of a RAID 0 failure increases in direct proportion to the number of drives, which means that the chance to lose data with an eight-drive RAID 0 array is eight times higher than with a single drive.
RAID 1 (also known as disk mirroring) increases reliability. The software or hardware controller mirrors the data on other drives, thereby cutting the chance of data loss by half. If one drive fails, all of the data is preserved on the other drive.
Unfortunately, storage capacity is also cut in half and write speed is much slower because the data has to be written twice. Also, because parity data requires disk space, a system's data storage space is less than the RAID's total capacity.
On a RAID 5 array, the data is written to all of the drives instead of being concentrated on a dedicated disk. For example, you can play a movie and pull a drive from the system, and playback will continue without issues or losses. If one drive in the system fails, the parity information can be used to reconstruct the data from the failed drive. All drives in the array system can be used at the same time, which greatly increases performance.
A RAID 6 array is essentially an extension of a RAID 5 array, with a second independent distributed parity scheme. RAID 6 provides an extremely high fault tolerance, and can sustain two simultaneous drive failures without downtime or data loss.
On Raid 1 (mirroring) the amount of available space is 50% of the total capacity. On a Raid 5 and 6, the amount of available space is (on average) 75% of the total available space of the drives, when used with 3 or more drives.
Current laptops have more than enough power to support HD video editing from cameras like the EOS 5D Mark II or the EOS 7D. However, when editors need to use Apple's ProRes 422 codec, along with Apple's Intermediate Codec (AIC), and demanding software applications like Adobe Photoshop, Adobe After Effects, Adobe Premiere Pro, Apple Final Cut Pro, or Maya 3D, hard disk bandwidth requirements increase so significantly that laptop-based, multi-stream, real-time editing is often not possible. A typical solution is to store all of the digital content on an external RAID that editors can easily access.
A common disk configuration for HD video editing is to have three hard drives:
- Hard Drive 1 = Operating System and Applications
- Hard Drive 2 = Video and Audio Files
- Hard Drive 3 = Export Files
Video editors tend to set Hard Drive 2 to RAID 0 for faster performance
A 1TB Hard Drive can hold up to:
- 84 hours of HDV 1080i
- 10 hours of ProRes 422 HQ
- 2.25 hours of HD 1080/60i
Keep in mind that having four 1TB hard drives does not mean that you have 4TB of hard drive space available. Parity data requires disk space, so a system's data-storage space is always less than the RAID's total capacity. Also, depending on the RAID level that you choose, you might see a significant reduction of available capacity.
Three typical examples of drive space are (actual capacity of specific drives and systems may vary):
- 4TB RAID (four 1TB drives) = 3.63TB of available space
- 8TB RAID (four 2TB drives) = 7.27TB of available space
- 12TB RAID (four 3TB drives) = 10.91TB of available space
Professional RAID systems offer a chassis that can hold up to eight drives and use load-balancing power management to divide the workload between two power supplies. This enables the system to continue working in the event of a power-supply failure. They support multi-stream HDV, DVCPro HD, XDCAM HD, ProRes 422, and uncompressed SD workflows, and they offer High-speed interfaces (eSATA, FireWire 800, FireWire 400, USB 2.0 or 3.0, and Thunderbolt).
Apple's Thunderbolt technology is a new, high-speed, dual-protocol Input/Output technology that is designed for performance, simplicity, and flexibility. This high-speed I/O technology is capable of delivering a blistering two channels of 10 Gigabits per second, per port of performance.
High-end RAID systems usually monitor and manage all aspects of the system, including the hard drives' health, RAID set controller, controller cache, fan, power supply, and enclosure temperature. A front-panel LED display provides visual feedback and an audible alarm signals a controller or drive failure. Some systems allow users to monitor and manage the RAID storage from anywhere (via TCP/IP) and can even send error notifications via email.
With the increasing resolution of today's still digital image files (especially RAW files), and of course the large size of original HD video files, selecting the right storage is often as important for photographers as deciding upon what cameras and lenses to use. Consider your needs in terms of files you currently have, as well as projecting months or years forward, and allow extra space for the inevitable added files you shoot, or possible file size increases if you move to different cameras. The beauty of the right RAID system for photographers is the peace of mind that comes with knowing not only that you've got space to hold your current files, but that they and the files you'll add in the foreseeable future are safe from the inevitability of a hard drive failure.
The CDLC contributors are compensated spokespersons and actual users of the Canon products that they promote.