Net booting RPi 3B+ constantly reading SD card

[minghia]

I have got my 3B+ to netboot but I have a problem where the system is periodically accessing the SD card, or at least that what I think it is doing. The green ACT LED is flashing every so often like a heartbeat. This affects audio play back. Every time the led flashes the audio drops out. If I install a blank SD card, the system boots as expected and my 1 minute sine wave file plays without any problems. Is there a way to stop the system constantly checking for a non-existent SD card?

Also the timeout before the system starts accessing the network is quite awhile in comparison to when the blank card is inserted. Is there a way to shorten the timeout before checking the network to start booting?

Tony

[epoch1970]

In reverse order,
No, you can't boot faster. You can boot a bit slower if the machine doesn't recognize your USB devices (or network), but that's all.

Are you sure the system tries to access the SD?
I suggest it syncs the contents of the NFS filesystem across the network, that takes time and interrupts other tasks.
Check your mounts do not specify option "sync" (you can add option "async" to be sure, normally is it selected by default)

[jerrm]

Are you sure the system tries to access the SD?

The SD polling when no card is present is well established, but completely undocumented.

What's worse, all that polling for the missing SD card wastes 10% of your CPU. Again, the Pi folks seem to think the wasted CPU isn't worth documenting.

Luckily there is a fix in the latest Raspbian. See: viewtopic.php?f=28&t=211912

[epoch1970]

Interesting. Thanks!