I have four second-hand Supermicro servers (X9DRi-LN4F+ in CSE-815TS cases). Each had five FAN-0086L4s (https://store.supermicro.com/index.php/40mm-fan-0086l4.html) that started failing. By failing, I mean the event log in the IPMI web interface contained entries such as:
369 ... FANA Fan Lower Critical - Going Low - Asserted
370 ... FANA Fan Lower Non-Recoverable - Going Low - Asserted
When I opened the case the fan was "stuck". I tried swapping the location of the fan but to no avail. Then more fans started failing -- eight fans out of the twenty across the four machines. I thought I might have a faulty batch so I replaced all twenty fans with this one: https://www.aliexpress.com/item/NIDEC-4056-R40W12BS5AC-65-12V-0-80A-4cm-For-SUPERMICRO-FAN-0086L4-Cooling-Fan/32806512302.html?spm=2114.11010108.01008.1.650c649bwYCBmG.
Now the new batch are starting to fail: three out of the twenty in the four months since I bought the replacements. What do I need to investigate next? The servers are located in a garage with a very small amount of dust: the fans and inside of the cases were visibly clean when I opened them. The temperature is in the 2-18°C range and humidity in the 40-70% range.