Comment by jlokier
4 years ago
I think at least 1-2 seconds.
I measured the performance of different size direct I/Os on some Samsung SSDs, and the write performance when switching from one test to another was significantly affected by the previous test parameters, or not, depending on whether a "sleep 2" was inserted between each test.
The only explanation I can think of is that the flash reorganises or commits cached data during that 2 seconds.
If you were using consumer SSDs, you have multiple layers of caching to worry about: in the controller's SRAM, and in a portion of the flash that's operating as SLC. There are also power saving modes to consider; waiting long enough for the drive to drop to a sleep state means you'll incur a wakeup penalty on the next IO.