1
Using for Capture and Playback
Blackmagic Design Applications
Using Blackmagic Disk Speed Test to check your disk (Mac)
If you want to check your disk array speed, Blackmagic Disk Speed Test can be run to check the array
speed, and to provide the results in video frame rates. This makes it much easier to understand
how various disk arrays will handle video capture and playback at various video resolutions and
frame rates.
Disk Speed Test provides more accurate results for large disk arrays, as often the manufacturer
provided speed results only check small data blocks, so you only get an indication of the cache
speed of the disk and not the sustained data rate of the disk. Video uses sustained data rates and
only Disk Speed Test provides a long burst of data for more accurate results.
When using Disk Speed Test, you need to account for disk seeking, so it’s best to add a healthy
margin to the results. If a disk array tests at 32 frames per second HD 1080, it doesn’t mean you can
do 29.97 HD capture and playback, as the margin is too tight. When checking the results, look at the
8 bit YUV 4:2:2 video sections, as intensity uses the 8 bit uncompressed video format.
Using the Apple Xserve RAID Disk Array
When you’re working with uncompressed HD video, your internal hard disk will not be fast
enough. In this case you need a high speed disk array, such as the Apple Xserve RAID. The Apple
Xserve RAID works great for both SD and HD when fully populated with 14 disks and at least 512 MB
of RAM for each RAID controller. For maximum performance and stable capture and playback with
uncompressed video we recommend the following settings:
Check
Use Controller Write Cache
Uncheck
Allow Host Cache Flushing
Check
Use Drive Write Cache
Uncheck
Use Steady Streaming Mode
Set “Read Prefetch” to
128 Stripes (8 MB/disk)
— If you observe dropped frames or jerky
video, try 8 Stripes (512 KB/disk) as recommended by Apple.
Note
: No single setting will work for all sizes and brands of disks.
These are the settings we have found delivers stable capture and playback with uncompressed
video. Other settings might also provide optimal performance and we recommend you check with
your local reseller before changing settings if you’re unsure of what these controls do.
Disk Speed RAID results after testing a disk array.
Apple Xserve RAID preferences.
