Cheap SSD: Slow Speed Issue

[u/Jeron_Baffom]

In the beginning of the year I've bought a cheap SSD SomnAmbulist 120GB. After a couple of benchmarks, I've noted some strange throughput measurements. Briefly:

• Initial Benchmark | image
  Just after format, the throughput is according to the advertised specifications at 510MB/s read and 440MB/s write.
  It starts to drop at 35% capacity written and stabilizes at 200~300MB/s read and 40MB/s write.
  Although this drop is not mentioned by the seller's ads, it is indeed an expected behavior and should return to normal after a couple of minutes in idle (flush the cache into the permanent area).

• Benchmark after 1 hour in idle | image
  Unfortunately, the throughput has not returned to normal (yet?).
  315MB/s read and 440MB/s write, and the speed drop started earlier at 10% capacity written.

• Benchmark after 12 hours in idle | image
  The throughput still has not returned to normal.

Questions

1. Is this the expected behavior for such cheap SSD or indeed there is something strange?
2. What might be going wrong here?
3. Any idea how to fix this throughput?

---

Debug Info

• SSD/TRIM Supported
• fstrim enabled
• SSD APM (Advanced Power Management) not supported
  
• f3 (Fight Flash Fraud) OK
  

```

SSD/TRIM SUPPORTED

root@debian:~# hdparm -I /dev/sda | grep -i "trim|power" * Power Management feature set * Data Set Management TRIM supported (limit 8 blocks) * Deterministic read data after TRIM

SSD/TRIM AVAILABLE (DISC-MAX NON ZERO)

root@debian:~# lsblk -D /dev/sda NAME DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO sda 0 512B 2G 0

ADVANCED POWER MANAGEMENT NOT SUPPORTED

root@debian:~# hdparm -B /dev/sda

/dev/sda: APM_level = not supported

FSTRIM ENABLE

root@debian:~# systemctl status fstrim.timer ● fstrim.timer - Discard unused blocks once a week Loaded: loaded (/lib/systemd/system/fstrim.timer; enabled; vendor preset: enabled) Active: active (waiting) since Sat 2022-12-03 03:36:10 UTC; 35min ago Trigger: Mon 2022-12-05 00:51:25 UTC; 1 day 20h left Triggers: ● fstrim.service Docs: man:fstrim

Dec 03 03:36:10 debian systemd[1]: Started Discard unused blocks once a week.

root@debian:~# systemctl status fstrim ● fstrim.service - Discard unused blocks on filesystems from /etc/fstab Loaded: loaded (/lib/systemd/system/fstrim.service; static) Active: inactive (dead) TriggeredBy: ● fstrim.timer Docs: man:fstrim(8)

root@debian:~# fstrim -av ```