Uncompressed (or lightly compressed) video needs lots of disk space. More than that, if you’re capturing live video, that disk capacity needs to be fast.

I’m using a Blackmagic Intensity Pro video capture card. It will capture 1080p uncompressed if your system can support that. It comes with a handy Disk Speed Test that measures read/write performance and translates that into frames per second of video at different formats.

In the original build of my video production box described in my previous post, I configured the two Hitachi Deskstar E7K1000 HDE721010SLA330 1TB drives as a hardware RAID 0 array with a 128K strip size connected to the onboard Intel ICH10R controller. Here’s what Blackmagic’s Disk Speed Test gave me:

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This is a stark contrast to running with older drives in the same configuration. Write speeds enabling 122fps for 8-bit 4:2:2 720p video should be more than enough for good captures. Running the DiskMark test that is part of PassMark Software’s PerformanceTest 7.0 indicated a sequential read rate of 222MB/s and a sequential write rate of 186MB/s.

For grins, I added another two 1TB drives to create a 4-way RAID 0 array with a whopping 3726GB capacity. The two new drives were a pair of Seagate Barracuda 7200.12 ST31000528AS, which have the same 32MB buffer as the Hitachi Deskstars. Running Speed Test again gave me:

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So in this configuration, it looks like I might be within spitting distance of being able to do 8-bit 4:2:2 1080p captures (even though the disk write frame rate measured 72fps, Blackmagic recommend a healthy margin and also SATA drives get slower the fuller they are). DiskMark indicated a sequential read rate of 341MB/s and a sequential write rate of 304MB/s.

I suspect that the only way I’m going to improve on this performance is to use a hardware RAID card with an on-board processor and dedicated memory.

Here’s the summary then:

2-way RAID 0

4-way RAID 0

8-bit YUV 4:2:2 1080p 54fps 72fps
8-bit YUV 4:2:2 720p 122fps 163fps
Sequential Read 222MB/s 341MB/s
Sequential Write 186MB/s 304MB/s