Debian supports all Orion based QNAP Turbo Stations. This includes the TS-109, TS-209, TS-409 and TS-409U.
Please be aware that Debian 10 was the last release to support these devices.
There are additional pages with instructions and information about all supported models:
Here is a table showing the differences between the supported devices:
|TS-109||TS-109 II||TS-209||TS-209 II||TS-409||TS-409U|
|CPU||88F5182 500MHz||88F5182 500MHz||88F5182 500MHz||88F5182 500MHz||88F5281 500MHz||88F5281 500MHz|
|RAM||128 MB||256 MB||128 MB||256 MB||256 MB||512 MB|
|Flash||8 MB||8 MB||8 MB||8 MB||8 MB||8 MB|
|USB 2.0 front||1||1||1||1||1||1|
|USB 2.0 back||2||2||2||2||2||2|
The Pro variants are the same hardware as the regular variants. They only differ in the software included in the original QNAP firmware.
Debian also supports QNAP's Turbo NAS devices, which are based on Marvell's Kirkwood chip.