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Understanding RAID | B&H Photo Video Pro Audio
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Understanding RAID

What you need to know for Post-Production Storage

By Ron Seifried

When it comes to editing, two basic questions editors ask is, "Where can I store all the footage that was shot?" and, "How safe is it?" Old school editors are used to the reliability of video or film, where they can "feel" what was produced in the field and have the peace of mind that comes with possessing a tangible, physical object that can be referred to more than once. Huge tape and film libraries are a testament to this method of working. But for the last decade, non-linear editing has become the mainstream method of working in a post-production suite. Capturing video into a computer and editing it on a timeline is the standard post work flow of today, yet it is sometimes difficult for artists to comprehend who are looking to capture, edit, and output in a secure work environment. It is important, when preparing any production and deciding how to properly go to post, to fully understand the options for storing data.

Video captured into a post-production workstation should be stored on a Redundant Array of Independent Disks or RAID. A RAID uses two or more hard drives simultanesouly for increased reliability and improved performance, utilizing larger storage space necessary for the larger file sizes of HD projects. RAID drives work in two ways: mirroring or duplicating data on two separate drives, or dividing the data across multiple drives. All the editor sees is one drive with one set of data files from their desktop.

Hot-Swappable Drives

By using multiple drives, performance and reliability are increased. If one of the drives fails in a storage array, a new one can be replaced without turning the system off, or a redundant drive can be used. The procedure to exchange drives without shutting down the system is called "hot swapping;" thus, those drives are referred to as "hot-swappable."

Most manufacturers of RAID's that can hot-swap a drive supply the drive with an attached sliding tray, like this one from Dulce Systems.

More is more when it comes to RAID configurations

Not using equal-sized drives in an array is an issue, determined by two factors: drive size and speed. With either factor, the smaller and slower will pace the majority. For example, in a RAID 0 or RAID 1 configuration, if you have four drives in an array, three of them 500GB and the fourth one 320GB, you will see the equivalent of four 320GB drives (1.28 TB) when the array is formatted. That represents 720GB of unusable storage space. If you replace the 320GB drive with a 500GB drive, you gain the full capacity of the other three drives. Storage capacity in an array is ultimately only as large as the smallest drive. Regarding speed, if there is one 7200rpm drive and three 10,000rpm drives in the array, the entire array will run at 7200rpm when it's formatted. It is very important that you use identical drives across the board when setting up an array for maximum capacity in your post-production suite.

RAID Levels

There are several different levels of RAID's. Some have limitations and features with which you should be familiar before purchasing and setting them up. Typically, only three are commonly used today (0, 1, and 5).

JBOD – stands for Just a Bunch of Disks. No redundancy or mirroing is involved in this configuration. The controller views each drive in the RAID as an individual disk.

RAID 0 – Known as striped disk, it is the least reliable of all the RAID options because it is does not use any level redundancy. Data is spread across all the disks in fragments, increasing speed. But because the data is spread over all the disks, they are read off the drive in parallel, so if one drive fails, everything is lost. Adding drives to the array increases bandwidth, but also increases the risk of data loss. One advantage of RAID 0 is that there is no loss in data capacity, meaning that if you have a 500GB spread across two or more drives, when formatted, the operating system will see 500GB. Please note that some OS's will see lower capacity depending on their file structure.

RAID 1 – also known as disk mirroring, this offers full redundancy. By putting data on the same two (or more) disks, the data is being read alternately from each drive. If one of the drives fails, an identical copy of the data remains on the surviving drive.

RAID 0+1 – Only available on arrays with four or more drives, this combines mirroring and striping for the increased performance of RAID 0 with the redundancy of a RAID 1. For example, when there are four drives, the first two will have data striped across them, and the second two will be a mirror of the first two. Because there are more drives used in this configuration, the cost increases along with the performance.

RAID 1+0 (aka RAID 10) – Similar to the RAID 0+1 in that it requires four or more drives, this method has the first two drives mirrored together, while the second set is a mirror of each other but stores the striped data of the first set of drives. Both sets are set up as mirrored drives. The advantage here is additional security over the RAID 0+1.

RAID 2 – Set up like a RAID 0, but requires an additional partition for the parity information and does not offer the read or write performances of a RAID 0. The old parity must be read before updating to the new parity, severely bottle-necking access times. A RAID 2 stores ECC info instead of the parity, but since all of today's drives have ECC, this method has become obsolete.

RAID 3 -needs to have all the drive spindles synchronized so when the disks are being read, each individual drive needs to be accessed. This configuration is also made obslolete by today's high-efficiency drives.

RAID 4 is also like a RAID 0, but requires an additional partition for the parity information and does not offer the read or write performances of a RAID 0. The old parity must be read before updating to the new parity, severely bottle-necking access times.

RAID 5 – another form of striped disks, this method combines three or more drives that protect data if one drive fails. One of the most secure ways to set up an array today, RAID 5 is also one of the most expensive. Only available by using a hardware controller card, this configuration stripes drives with parity for data redundancy. Parity is a binary math that, in the event of failure allows one replacement drive to rebuild the data, lost from the remaining drives on the array. Because of the need to utilize parity for data redundancy, three 1GB drives in an array will be visible as only 2GB on the desktop. For a RAID 5 setup, storage space is sacrificed for increased security. By hot-swapping a defective drive with a replacement, the controller will take time to rebuild the array and can decrease performance, but the data will remain intact.

RAID 6 – Similar to RAID 5, it can recover data if two drives fail. The cost factor greatly increases with a RAID 6 config, due to the need for two parity-dedicated drives.

MODEL CAPACITY INTERFACE # of Drives HOT-SWAP­PABLE RAID PRICE RANGE
CalDigit Firewire VR
500GB - 2TB
Firewire 800/400 & USB 2.0
2
Yes
0, 1, JBOD
$295.95-$949.95
G-Tech G-RAID2
500GB - 2TB
Firewire 800/400 & USB 2.0
2
No
0
$338.95 - $774.95
CalDigit S2VR
500GB - 2TB
3Gb eSATA
2
No
0, 1, JBOD
$548.95- 1,528.95
Lacie Biggest S2S
1.25TB - 5TB
3Gb eSATA
5
Yes
0, 0+1, JBOD
$999.95 - $2,549.95
Dulce Systems HD Commander
1.25TB - 5TB
3Gb eSATA
5
Yes
0, 1, Span, JBOD
$1,749.95 - $5,578.5
Ciprico MediaVault U320-R
1.25TB - 2TB
SCSI 320
5
No
0, 3
$2,499 - $3,199
Ciprico MediaVault 4105
1.25TB - 5TB
4Gb Fibre Channel
5
No
0, 3
$3,099 - $6,499
Ciprico MediaVault U320-RX
2.5TB - 5TB
Dual Channel SCSI 320
10
No
0, 3
$4,799 - $6,999
Ciprico MediaVault 4210
2.5TB - 10TB
4Gb Fibre Channel
10
No
0, 3
$5,899 - $12,499
RAID 5 support & higher
G-Tech G-SPEED eS
1TB - 4TB
3Gb eSATA
4
Yes
0, 1, 5, 10, JBOD
$898.95 - $2,749.95
Lacie Biggest Quadro
2TB - 4TB
eSATA, Firewire 800/400 & USB 2.0
4
Yes
RAID 0, 0+1, 5, 5+Hot Spare
$979.95 -$1,999.95
Dulce Systems Quad-e
1TB - 4TB
Two Quad Channel SATA II
4
Yes
0, 1, 3, 5, 6, JBOD
$2,149.95 - $4,998.50
G-Tech G-SPEED
1.5TB - 4.5TB
4Gb Fibre Channel or SCSI 320
6
Yes
0, 1, 0+1, 3, 5, 6, JBOD
$2,848.95 - $4,748.95
CalDigit HDOne
2TB - 8TB
PCI- Express
8
Yes
0, 1, 5, 6, JBOD
$2,189.95 - $7,599.95
CalDigit HD Pro
2TB - 8TB
PCI- Express
8
Yes
0, 1, 5, 6, JBOD
$3,595.95 - $10,899.95
Dulce Systems Duo Quad
2TB - 6TB
Dual Quad Channel SATA II
8
Yes
0, 1, 3, 5, 6, JBOD
$3,999.95 - $6,998.50
Dulce Systems Pro DQ
2TB - 8TB
Two Quad Channel SATA II
8
Yes
0, 1, 3, 5, 6, JBOD
$4,448.95 - $9,799.95
Ciprico MediaVault 5108
2TB - 8TB
PCIe extender to SATA II
16
Yes
0, 1, 1n, 5, 10, 10n, 50
$3,999.95 - $9,349.95
G-Tech G-SPEED XL
3TB -16TB
4Gb Fibre Channel or SCSI 320
16
Yes
0, 1, 0+1, 3, 5, 6, JBOD
$6,998.50 - $14,997.50

Hardware and Software RAID

There are two factors that need to be understood when setting up a RAID. A hardware RAID uses a controller card to connect to the internal or external set of drives for increased security and speed, while a software RAID utilizes a program, or in most cases today, an operating system to set up. To receive the full benefit, it is necessary to create a RAID through a hardware controller card.

Hardware RAID controller cards come in several different configurations, from manufacturers like Atto.

With a hardware RAID, the controller card does all the work, leaving the CPU to multitask with other applications. Some motherboards have built-in RAID 0 and 1 controllers, so it may be unneccessary to incur the cost of a controller card. Hardware RAID's always have some kind of software interface for system administration. B&H carries a wide selection of hardware controller cards that support several different levels of RAID and interfaces.

The less expensive method is to set up a RAID through software-only applications, most commonly found in today's operating systems. But you get what you don't pay for, as software RAID's will eat up the computer's perfomances, sometimes severely hampering processor-intensive tasks. The main adavantage here is the cost-effectiveness of setting up a software RAID. As much as 10% of the system performance can be effected when working with a software RAID, so you need to be conscious of what type of productions and how much system resources are required before deciding how to configure a post-production studio.

There are many third-party manufacturers that have external hard drive RAID systems that come with controller cards, and accessories including hot-swappable drives, power supplies and cables. You can easily set up an internal array for a Mac Pro, PC workstation, or an empty external array case, but you need to be aware of how many drives the computer case can add on, and what type of controller card can be used (PCI Express or PCI-X). The rule of thumb when setting up your own array is that all of the drives should be the same model, brand, size, and speed. Remember: When mixing size and speeds in an array, the overall performance can be hampered.

Conclusion

There are several ways to approach building a storage solution for post production. If you are shooting a film, documentary, or other long-form productions and are reusing flash memory cards like P2 and SxS, then it is very important to have a secure RAID system in place with parity drives and the ability to rebuild like RAID 5 or 6. Otherwise, when the drive fails, all of the data that was captured will be gone completely. When using a video tape or optical disc recording method, it is not as imperative to have a secure RAID solution, as all of the data can be recaptured into the editing system if there is a drive failure, provided the project file is intact. Either way, it is always important to have some type of separate backup system in place to ensure that all of the hard work you put together in the field can be accessed again in post.

Please email feedback on this article, or suggestions for future topics, to videofeedback@bhphotovideo.com