Last week I bought a DNS-315 NAS from a guy that didn’t know how to use it. The idea is to put all the multimedia stuff on it, buy an additional Android-TV box, this way my home computer doesn’t have to be powered on every time my son asks to view a cartoon.

The first thing I did (just like the quick install guide says) was to open the box. Well, I opened it maybe a bit too wide, took out the mainboard and studied it a little 🙂

Well, the CPU is more or less bearable. The SOC is a PLX NAS7820 chip which contains a dual-core ARM11 CPU at 750Mhz (Linux’ shows 300 “BogoMIPS” but I assume that’s because at early startup, when “BogoMIPS” are measured, the CPU isn’t running at full speed – my Galaxy S5, for example, shows 48 “BogoMIPS”, for Snapdragon 801).

It contains a Oxford Semiconductor OX820 SATA 3G/s controller which can sustain 48Mb/s when directly reading from the Seagate Video 2Tb HDD I inserted (which shows about 190Mb/s sustained being connected to a PC).

Plus an USB 2.0 port which can be used to connect USB HDDs/flash drives and, possibly, other types of USB hardware (that depends on how kernel’s configured).

And last but not least, it has a Gigabit Ethernet controller. With iperf I was able to measure about 760 MBits when sending data from NAS to PC and 488 MBits in the reverse direction; in both cases the limiting factor was the NAS CPU as it goes up to 100% on one core (and the second core is not used at all); I suppose iperf does some checksumming of the sent/received data; if it wouldn’t, the PC->NAS numbers would be much higher.

Also, as you can see from the product brief (available if you click on “NAS7820” above), the SOC contains a “Network offload engine” which, as far as I understand, can pump data directly from hard drive to network and back, thus substantially rising file server performance. More on this later.

Some researcrh revealed that there are similar products from other vendors, namely Medion Life P89626/P89630/P89635/P89636 aka NSA-212 and some Zyxel NASes are using the same SOC, so they should be compatible to some extent at hardware level; they use different software though (the proprietary D-Link web-interface and all related stuff), although the Linux kernels should be similar.

Here’s a photo of the mainboard, top and bottom:

At bottom-right you can see a 4-contact unsoldered connector which is, I guess, console UART. One of the pins is connected to GND plane, one is unconnected, and the two other are, I guess, RX and TX. Will try that some day, perhaps.

2 thoughts on “Hacking D-Link DNS-315 NAS 1: hardware

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