Connecting a serial console cable to the DS-101/DS-101g+
The Synology DS-101 and DS-101g+ already has the header for the serial console soldered on, so there's no need to dig up your soldering iron just to get debug output! The only thing you need is a 3.3V TTL Level serial cable. There are several ways to get this. Look at the NSLU2-Linux serial port guide for information about the cable.
It is relatively easy to build such a cable oneself based on a MAX232 and a few other components on a breadboard. See the fotos at http://helgen.oinkzwurgl.org/diskstation/rs232/ to see how. Or ask google about a "max232 circuit".
The serial port is marked with COM1 & JP6 on a DS-101 and COM1 & JP2 on a DS-101g+/DS-106. On the DS101J, the serial port is probably JP6. This has still to be confirmed. On the CS406 (Rev. 2.2) the port is labeled JP1 and is located near the SATA ports. The pinout is as described below.
The pinout is as follows: