Disk Arrays for Uncompressed SD Video
What kind of disk do I need for uncompressed SD video?
Although it's possible to work with JPEG and DV video on the internal IDE or SATA disk that's standard on all computers, uncompressed video uses higher data rates, and requires special consideration for disk storage.
Uncompressed video is great quality, however the data rates are higher than commonly seen on computers, so a single hard disk is not usually fast enough for reliable capture or play back of uncompressed video. The solution is to use multiple hard disks, working together so they are much faster.
Disks are "striped" together to build an array of disks. Striped disks work together to store the data and so the overall data rate per disk is much lower. This stresses each disk less, and you can store higher data rates than a single disk can handle.
You can get all kinds of disks, and these vary in speed. You can get a simple disk box and place a few hard disks in it, or you can even put the disks internally in the computer if space is available. The types of disk arrays where disks are connected together are commonly called JBOD, or "Just a Bunch Of Disks" arrays. Other terms for JBOD include "hard drive chassis" and "disk array chassis". Basic JBOD's often have no obvious brand name but more sophisticated ones will have brand names, eg Infortrend EonStor.
You can then create a striped RAID from these disks using software such as Disk Utility in Mac OS X, or the Computer Management control panel in Windows XP Pro. These disks will then appear on your system as a single disk. You can then select this as the capture location in your video capture software.
PCI Express Disk Arrays
CalDigit HDPro disk arrays are highly recommended because they connect directly to the PCI Express bus of Mac Pro computers, just like Blackmagic Design Multibridge products. This means you can take advantage of the full speed of the PCI Express bus without the cost and latency associated with traditional HBA cards such as SCSI, Fibre Channel and FireWire cards.
SCSI Disk Arrays
Recommended disks for building disk arrays are Seagate™ Cheetah™ Ultra 160 or Ultra 320 SCSI disks. These disks are fast, and work great for real time effects. For single stream simple capture and playback up to 10 bit uncompressed standard definition, you can use 2 Cheetah disks. For dual stream real time effects such as dissolves, 4 or 6 disks may be required. Ultra 320 SCSI disks are much faster and have now largely replaced Ultra 160 SCSI disks.
Mac's don't come with Ultra 160 SCSI or Ultra 320 built in, so to connect SCSI disks you will need to add in a SCSI card. We recommend the ATTO UL3D dual channel Ultra 160 SCSI card for use with G4's, the UL4D dual channel Ultra 320 SCSI card for G5's with PCI-X slots and the UL5D dual channel Ultra 320 SCSI card for G5s with PCI-Express slots. Please ensure that you have downloaded and installed the latest ATTO firmware and driver updates for compatibility with the latest systems.
Some "server class" Windows PC's include SCSI as standard but otherwise you will a SCSI card. If your PC has PCI-X slots, it would be best to use an Adaptec 39320A-R card.
IDE/ATA/SATA Disk Arrays
Another disk solution for uncompressed video is the IDE prebuilt disk arrays. Unlike JBOD disk arrays you build yourself, prebuilt hardware RAID disks can offer hardware protection for video data in case of a disk fault. If a disk fails, the disk array keeps working until you can get the disk fixed, and valuable data is not lost.
Huge Systems make a range of disk arrays which are fast and low cost. We have tested both their U160 and even faster U320 models and they work great. The disks are IDE but connect to the Mac or PC in a SCSI chassis and so should be partnered with a SCSI card.
Disk arrays from Medéa are also popular and it is a good idea to check Medéa's website for compatibility information, especially in relation to PowerMac G5's and Mac OS X 10.3 and 10.4.
We also recommend the Apple Xserve RAID, and this works well for uncompressed video. These connect to the Mac with a Fibre Channel card such as the Apple Fibre Channel card. We recommend increasing the RAM cache to 512 MB of RAM per channel for use with uncompressed video.
Some Windows PC users create a disk array of 4 IDE or SATA disks which fit inside the PC chassis and connect to the existing IDE or SATA bus. Four IDE disks is the minimum which should be used for uncompressed 10 bit standard definition video.
Is My Disk Array Fast Enough?
Because disk systems are always changing, the best recommendation for disk array options is your dealer. Often dealers will know of other lower cost, and faster disk solutions because they can keep up more easily with the many brands and options available worldwide.
DeckLink users can run the Blackmagic Disk Speed Test application which is included with the DeckLink driver software. This utility takes measures the speed of your disks and displays how many frames per second of video you could do in standard definition (NTSC & PAL) and high definition. We recommend testing your disk array with Blackmagic Disk Speed Test as many other disk utilities do not take in to account factors such as the RAM cache which may be used in some disk arrays. Blackmagic Disk Speed Test can be used on any Mac or PC which has a DeckLink card.
Additional Information
Host Bus Adapters (HBA)
• ATTO SCSI and Fibre Channel cards
• Adaptec SCSI and SATA cards
Prebuilt Disk Arrays
• CalDigit
• Huge Systems
• Medéa
• SANman (Australia)
• Xserve RAID
Disk Arrays - components
• Infortrend EonStor, disk array chassis
• Seagate hard disks
