Capture Card Recording
|Overall Statistics||Capture Card Recording|
|Data Read||8.56 MB|
|Data Written||487.85 MB|
|Disk Busy Time||1.88 s|
|Average Data Rate||262.65 MB/s|
Many folks still use capture cards to transfer video from camcorders or record television programming fed into their PC. They're also still important for console gamers interested in preserving their own highlight reels.
Our trace represents a the workload you'd encounter while using one of the latest-generation capture cards, such as Black Magic's Intensity Pro (pictured above) or Hauppauge's Colossus (a pair of cards we happen to have in the lab). It might be natural to assume that writing a video stream to storage would happen sequentially, but that actually turns out to be false.
The capture card has to buffer video from the source, which is why ~40% of the data transferred is random in nature. Buffering also explains why a majority of the trace sees outstanding I/O operations higher than one, as the capture card simultaneously accesses the buffer while recording to a separate video file.
- 34% of all operations occur at a queue depth of one
- 55% of all operations occur at queue depth between two and eight
- 59% of all data transferred is sequential
- 20% of all operations are 4 KB in transfer size
- 49% of all operations are 128 KB in transfer size