From NAS-Central Buffalo - The Linkstation Wiki

Contents 1 Led Description 1.1 Power LED (green) 1.2 LINK/ACT LED 1.3 DISK FULL LED (red) 1.4 DIAG LED (red)

Led Description

Power LED (green)

on	Normal
Blink	At bootup, prior to ppc_uartd starting, Just prior to ppc_uartd starting to write to flash memory
Blink Slowly	Setting timer

If ppc_uartd is not started for some reason, it remains blinking, and then after few minutes, DIAG LED blinks 6 times(hard disk error), 6 times, 6 times, ... finally the box shutsdown.

LINK/ACT LED

orange	10BASE-T
green	100BASE-TX
blue	1000BASE-T(only HGLAN)

DISK FULL LED (red)

on	Disk full
blink	Writing to flash memory

DIAG LED (red)

3 times blink	Partition warning: /dev/hda3 is not mounted on /mnt. You can ignore it.
4 times blink	Problem with the cooling fan - probably rotor jammed.
5 times blink	Problem with the flash memory*
6 times blink	Hard drive not found. Or ppc_uartd is not running.
7 times blink	Problem with the RAM/LAN/HDD controller.
blink many times	Writing to flash memory.

   * Sometimes, you can recover from a flash memory error by pulling out power cord and try again after one night.

Table copied from http://www.yamasita.jp/linkstation.en/led.html with minor rewording. nobuakiy helped with the translation.

Notes Users have reported problems when the drive already has a Linux partition on it - the diag light blinks 6 times. The solution appears to be to simply to reformat the drive.