Disk Arrays for Uncompressed HD Video
What kind of disk do I need for uncompressed HD video?
Although it's possible to work with JPEG, HDV and DVCPRO HD on your internal IDE or SATA disk that's standard on all computers, uncompressed video uses higher data rates, and requires special consideration for capture disks.
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.
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 HD disk arrays are currently the Seagate Cheetah Ultra-320 10k.6, Ultra-320 15k.2 or the Maxtor Ultra-320 10k drives. We don't recommend Ultra-160 drives for uncompressed HDTV work.
We recommend 8 x 10k drives or 6 x 15k drives when building an array. However, you can go as low as 6 for 10k and 4 for 15k; however the extra disks will help improve performance as the drives fill to capacity.
The recommended drive enclosure for building disk arrest for HDTV is any JBOD (Just a Bunch Of Drives) case with two separate SCSI buses with half the drives connected to each bus. Both buses should be striped together for maximum performance. The manufacturers we currently recommend are: JemsData and Nstor. There are many others as well, however you do need to make sure they have two independent SCSI buses and use the recommended SCSI drives.
You also need a high performance Ultra 320 SCSI card.
On Mac OS X we recommend the ATTO UL4D (PCI-X) or the UL5D (PCI-Express). The data throughput can be over 500 MB/sec for DeckLink HD series cards on a PowerMac G5 which is very fast, so you need to use the latest Mac OS X and ATTO driver. Ensure you have downloaded and installed the latest UL4D firmware and driver updates for compatibility with the latest systems. The UL4D / UL5D is perfect for use with DeckLink HD series cards.
Adaptec have discontinued development of their SCSI drivers and firmware for the Mac OS. Accordingly we recommend the use of SCSI cards from ATTO Technology as they have a proven history of reliability. Other brands of SCSI cards might work OK but we have not tested them.
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 U320 models and they work great but the U320 units are more appropriate for use with HD video. The disks are IDE but connect to the Mac in a SCSI chassis and so should be partnered with the ATTO UL4D SCSI card.
Fibre Channel Disk Arrays
The Apple Xserve RAID (Mac only) works perfectly for both SD and HD when fully populated with 14 disks and at least 512 MB of RAM for each RAID controller. Please see "Can I use an Xserve RAID with a G5 and DeckLink HD?" for detailed information.
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
www.caldigit.com
www.attotech.com/support.html
www.hugesystems.com
www.seagate.com
www.apple.com/server/storage/
www.maxxdigital.com
www.lacie.com
