If you look at their lab [0], it seems his NAS is separate from his kubernetes nodes. If he hasn't tuned his networking and NAS to the maximum, network storage may in fact add a LOT of delay on IOPS. Could be the difference between fractions of a millisecond vs actual milliseconds. If your DB load is mostly random reads this can really harm performance. Just hypothesizing here though, since it is not clear whether his DB storage is actually done on the NAS.

[0]: https://dizzy.zone/2025/03/10/State-of-my-Homelab-2025/