I think I’ve figured out what is limiting the write speed of our PC for high speed imaging. As mentioned before, we have four Intel 520 SSDs in RAID 0. These drives are benchmarked to write at about 500 MB/sec, so four of them should be capable of ~2GB/sec, yet we only see about 960 MB/sec. What’s going on here?
Today, I looked at the performance of an individual drive. Using CrystalDiskMark, we only get about 240 MB/sec sequential write speeds, which is far short of the claimed 500 MB/sec speed. The reason turns out to be that we are benchmarking with 4GB writes of random data, and the claimed speed for the Intel 520 SSD assumes you are writing compressible data. Indeed, if we switch to benchmarking with data that’s all 1’s, the speed increases to ~480MB/sec. Unfortunately, our images are going to be pretty close to random data, so the random benchmark is probably much more appropriate.
Fortunately, there are other SSDs out there that perform much better writing incompressible data, such as the Samsung SSD 840 Pro. These use different controllers that don’t rely on compression to achieve their fast writes and so are more appropriate for our use case. I’m going to see if we can replace our Intel SSDs with the Samsung SSDs. Hopefully that will get our speeds well above 1.1 GB/sec.