![]() I ran into this in this series of tests, as my M1 Mac mini doesn’t have many large files which I could readily read between writing and reading back the same test file. The problem is with read caching, where macOS, having just written a file, keeps it in memory, so when it comes to read that file back it doesn’t fetch it from storage but from memory instead. Although repeated writes can become slightly faster, they seem consistent through each batch of tests. Determining what actions are necessary to ensure that caching doesn’t make results incorrect is clearly an important matter.įrom these and previous tests, it appears that my code doesn’t run into problems with write caching. In my first set of tests, I steered clear of that by performing 19 write and read operations between each test in which a file which has been written has been read back. That’s an important step forward.įrom the outset, I’ve recognised the threat posed to performance testing by macOS’s obsession with caching everything it can. I therefore conclude that, whatever Stibium is measuring is closely correlated with generally-accepted performance of a range of SSD media. Again, these are of the order which I have come to expect from other benchmark apps. My Samsung X5 500 GB SSD running over Thunderbolt 3 delivered value for money, with a read speed of 2.1 GB/s on the T2, and write speeds of 2.3 GB/s (T2) and 2.1 GB/s (M1). Putting the same class SSD into an OWC ThunderBay 4 TB3 enclosure improved performance on the T2 iMac Pro, with a read of 569 MB/s, and writing at 539 MB/s. The M1, though, wrote at 392 MB/s (I don’t have a reliable read speed for the M1, though). The T2 read at 476 MB/s and wrote at 511 MB/s, which is of the order I had expected. When accessing an external SATA 6.0 Gb/s SSD over USB-C, the M1 was significantly slower when writing. The T2 read at 2.1 GB/s, against the M1’s 3.5 GB/s, and the T2 wrote at 2.7 GB/s against the M1’s 3.4 GB/s. On my T2-equipped iMac Pro, internal SSD performance on 1 GB files was consistently good, but slower than on my M1 Mac mini. I therefore set out to measure single read and write transfer rates on 1 GB files on a range of different storage types I have to hand. Included within that is the Swift code which I am using to perform read and write tests.Īlthough benchmarks for internal SSD storage in different Macs may be a matter of discussion, there’s good consensus on the performance of external storage. There is an important point when using Mach ‘ticks’ which can get you into trouble if you don’t apply the correct timebase scaling to convert from Mach ticks to time units: on Intel processors, the scaling is 1 so is often ignored, but that’s very different when running native on an ARM processor.Īnyone wanting to try out Stibium should also welcome the fact that this new beta has a simple styled text Help page now. Encouraged by my initial results from a very early beta-test version of my utility to measure the performance of storage systems, Stibium, I have been progressing its development and looking at whether its results make sense.īeta 3 now uses Mach absolute time rather than the system clock, so it should be more accurate in measuring smaller time differences.
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