[TangerineSDR] Maximum storage write speed of Odroid N2, etc.

[David Witten]

There was some speculation about storage interfaces available on the Odroid
N2 on last night's Teamspeak session.

For those who are interested, some information is available:

The N2 does *not* have an M.2 interface to directly support NVME Solid
State Drives (SSDs).

It appears that currently available CPUs available from AM Logic (AML)
currently only present 1 lane of PCIe 2.0 for use by board designers.  This
is most frequently committed to supporting USB 3.0.  (or perhaps 2, with
one used to support 1Gb Ethernet)

A simple graphic benchmark of USB write speed is shown under the heading
"USB 3.0 hosts":
https://www.hardkernel.com/shop/odroid-n2-with-4gbyte-ram/ , which shows
write speeds varying dramatically with block size.,

Further down the page are tables of "eMMC storage performance"  and
"Micro-SD UHS performance".

It seems that the fastest write performance available in this environment
(other than using an inherently size-limited RAM disk) is:

   1. to use a USB 3.0 connected external device that either converts to an
   M.2 NVME interface supporting a NVME SSD,
   2. or a USB 3.0 device to emulate SATA to support a spinning disk.

Other boards in this price range support other options.  The two most
visible options I have found are:

   1. Boards using the Rockchip’s RK3399 processor, which is arguably
   slower (2 big + 4 little cores) but which supports 4 PCIe lanes + native
   support for 1Gb Ethernet and USB 3.0 simultaneously.  THis is available
   from several board suppliers, and most configurations support M.2 NVME.
   eg.: https://www.khadas.com/product-page/edge-v
   2. The NVIDIA Nano module, which supports almost all desired interfaces
   in spades, but again is supported by a less potent quad-core A57 supported
   by the 128-core Maxwell™ GPU.  Only M.2 Key E is available on the
   developer kit which is not usually used to support storage devices.  But
   everything is available on the module edge connector,an all desired
   interfaces can be used simultaneously. eg:
   https://developer.nvidia.com/embedded/dlc/jetson-nano-product-design-guide

Dave, KD0EAG
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