So - 0.5PB written and time to move on to stage 3 of the test. For the next stage, we will half-fill the disk with a single large static file and then repeatedly fill the rest of the SSD with a second file. This will exercise the controller as it tries to balance wear across the whole of the flash, moving the static file around in the background, and should lead to more visible write amplification.
Test setup is very simple. The static file is created with:
# dd if=/dev/phony of=/data/static bs=1G count=476 oflag=direct 476+0 records in 476+0 records out 511101108224 bytes (511 GB) copied, 1863.89 s, 274 MB/s
And the test to be run repeatedly is:
dd if=/dev/phony of=/data/abc bs=1G count=476 oflag=direct
Once this has written approximately another 150TB, we will recalculate disk lifetime and write amplification and see how it compares with writing to an empty disk. It shouldn't take too long so check back soon.