NDAS implementation

Version: N/A

Status: N/A

Description

NDAS (Network Direct Attached Storage) is Ximeta Corporation's patented technology "which enables all digital storage devices (HDD, ODD, Memory, Tape Drives) direct connection into standard Ethernet networks." The main difference is that while NAS devices generally use common network protocols such as SMB/CIFS (Samba or Windows Networking) or NFS (Unix's Network File System) over IP to act as a fileserver on the network, NDAS has its own proprietary protocol called LPX (Lean Packet eXchange) which works at the Ethernet frame level.

Using NDAS, the MG35 is seen by the PC as another local harddrive, and the filesystem details are managed by the PC.

Normally, NDAS is implemented in hardware via a chip manufactured by Ximeta. The hardware implementation allows very fast file transfers since the chip handles directly the Ethernet frames, avoiding the header processing CPU overhead and by removing the need for TCP/IP headers. The chip also talks directly to the disk, bypassing the OS and increasing the read/write speeds to the disk.

On the MG-35, however, the NDAS functionality is emulated through software via a device driver licensed from Ximeta. The use of software emulation on the slow processor of the MG-35 means that NDAS network transfers are really slow. The need to emulate the network functions via software also means that the direct disk access is lost, negating both of the performance gains of the NDAS chip and decreasing performance. According to Altech's support forum, NDAS maximum speed is 15Mbps.

In the old versions of the firmware (probably all the 1.4.x series?), the software emulation consists of two drivers: the ethernet protocol (LPX) and the block device translator (NDEMU). The ndemu.o kernel module talks to the disk and acts like a block device. It hands over device data to lpx.o which transmits the packets over Ethernet in a proprietary format.

In the 1.5.x firmware, the NDAS modules are ndas-core.o, ndas_emu.o and ndas_sal.o.

The remote system (the PC) also has an LPX protocol driver to receive the packets and hands those off to a virtual scsi driver. NDAS's LPX protocol also seems to be encrypted (looks like 128bit). Encryption and decryption is also handled by the ndemu.o module.

License

Proprietary, Ximeta

Todo

History

Comments

"If anyone is interested in building the NDAS modules from sources, a possible starting point can be the OpenWrt port."

• That's a mips binary library in there. The identical version (for arm) is in the repository. What is this link for?
  • That page shows the procedure to build from sources. The tar.gz from here contains the NDAS sources. Not that I can see any point in porting it :)