Slow writes to SSD

Keith W

New Member
So here's the story: I have a 500GB 970 Evo Plus NVMe, about 40% full on the motherboard as a C:\ system drive. Works as quick as the board/CPU/RAM (ASUS 970 gaming aura, FX8350, 16GB) will let it. It's only PCIe 2. It's still quite quick. 1.4GB/s read, 1.1 write (seq) from Crystal Mark

Also have a Cruicial CT240BX500SSD1 SATA ssd, about 60% full of crap plus an old bootable OS on it, as E:\ drive on SATA (3) port 1.

All BIOS stuff is, hopefully set up ok. Running win10 1909.

Problem: When I write to the Crucial ssd, E, from the Samsung NVMe, C, the write rate starts off stonking (1GB/s) rapidly falling off after about 3GB to about 400MB/s for a while. If I try this exercise with a 16GB file after a clean boot the 400GB/s phase lasts to the end. Quick enough. If I've run anything which has left its trail of debris in my RAM it will drop off to as low as 6MB/s at times towards the last l GB or so. Too slow. Paging ???

I have a load of magnetic SATA drives for general crap and the speed from/to all of them is as expected i.e. 120 - 150MB/s

If I do a big one (37GB, C:\ > E:\ ) I get the same picture as above but the slow phase kicks in earlier and persists to the end. On one test, average transfer rate is just 68MB/s. Worse than between the magnetics or mag to ssd.

Why ?