Data is constantly moved around on an SSD to create larger free blocks in anticipation of a write request. Unlike a hard drive that can simply write data over the disk regardless of the content already on a platter, a cell must contain 0 before new data can be written, so it's an erase-write operation, not a write only. On a BMD camera, a bit slower means dropped frames on recording and freezes on playback.Īll SSDs require provisioning of additional space unavailable to the user to manage the garbage collection and housekeeping tasks. That's much different than a computer where an application can usually wait for an operation to complete with your user response just being a bit slower. The Digistor consumer drives are optimized to work in a video application with continuous reads or continuous writes and certified to work with the BMCC cameras. The data controllers available use different techniques to improve performance in a typical computer use with a mix of sequential and random reads and writes of various block sizes. If you only filled a consumer SSD to 50% capacity, you'll see the higher speeds since only the first level cells are filled. The speed of the first cell writes is the same as writing to the original single-level cell SSDs (SLC) but now only very expensive SLC SSDs exist and would most likely be for enterprise use. When MLC was introduced primarily to reduce the cost of SSDs, the speed of writing the second level cells was one-half the speed of writing to the first level cell. The consumer SSDs are likely all multi-level cells (MLC) which means the SSD controller is writing to all the first level data cells before it writes to the second level cells. That's why the Blackmagic Speed Test is important (and possibly the AJA data test as well but they often vary) because it stresses your storage device the way video does-long uninterrupted writes and reads of large blocks. Block size and the sequential versus random mix of I/O affect the speeds but again, they don't usually tell you how they tested. The manufacturers usually don't specify the block size they use when rating their drives. The manufacturer rated speeds are assuming compressible data and generally you can divide the rate in half as you mentioned.
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