[Nexus 7 Q&A, Help & Troubleshooting] bftb0:
Last night I transferred GBytes of data via ADB (i did a full tablet wipe and a bunch of restores) and couldn't help but notice that sustained data transfer via (wired) ADB is only about 1.4 Mbytes/sec. Sort of pathetic waiting around for a half-hour to transfer a 2.5 GB file.

Anyway, not to jack the OP (which is about WiFi), but I wanted to try and figure out what my best options are for high-speed backup (I have a 32 GB N7!) - including WiFi as an option.

Ran a couple of file transfer trials this morning using a ROM file that was 150,137,068 bytes.

Results first, more detail on each setup follows. (The results are compared in terms of data payload per second; in the cases where protocol overhead is high, the wire-speeds would be higher than calculated)

[1] SMB/CIFS write via WiFi : 518sec => 2.32 Mbits/sec. UGH (best of three trials)

[2] FTP put via WiFi : 109sec => 11.06 Mbits/sec

[3] FTP get via WiFi : 121sec => 9.9 Mbits/sec

[4] adb pull via USB : 78sec => 15.4 Mbits/sec

[5] adb push via USB : 117sec => 10.3 Mbits/sec

[6]* OTG VFAT write via USB: 33sec => 36.4 Mbits/sec

[7]* MTP copy via USB 13sec => 92.4 Mbits/sec

In the WiFi cases:

- Linksys WRT54G (802.11g) router circa 2006 [ 802.11g theoretical bw 54 Mbps ] 6' away -35 dBm signal

- SMB/CIFS "server" Windows Xp SP3 laptop on 100 Mbps Ethernet segment attached to router

- N7 SMB client app ES File Manager

- FTP Server app (Andreas Liebig) on N7

- FTP client app Windows Xp default ftp app for both push and pull

- Windows box on Ethernet, N7 only on WiFi.

In the OTG case:

- 8 GB Sandisk Class 2 microSD card on a card reader attached to OTG cable; single partition, empty card, VFAT formatting.

In the ADB case:

- adb v 1.0.31, Win 7 Pro x64, Quad-Core i5, USB 2.0

Observing the WinXp task manager performance tab during CIFS or FTP transfers, the wired (Ethernet) link would show a high degree of variability, oscillating between 5 Mbps to 15 Mbps instantaneous rates. Hard to say whether this is a router performance issue or something else (11 Mbits/sec approaches 1000 pkts/sec at a MTU of 1500 bytes).

* The numbers for the OTG and MTP transfer tests are possibly questionable as the role of file caching is unknown - the times given here are only the times that the file transfer dialog(s) remain on-screen. (The writes could be completing in the background out of cache with nothing showing on the screen) In particular, note that the OTG copy involved a "Class 2" microSD card - and yet the write speed seemed closer to 4.5 Mbytes/sec, rather than 2 Mbytes/sec

The SMB/CIFS transfer times are quite pathetic; but as with all performance measurements, any participant in the test could be the long pole in the tent. For instance, the issue might be the ES File Manager app. I did not test with a N7 CIFS-capable kernel.

Also, it would also appear that performance of ADB for file transfers are quite poor - well, in comparison to MTP anyway. Too bad MTP doesn't preserve file timestamps (as well as all sorts of other oddities).

Apologies in advance for using file transfer as a network benchmarking method - my connection to the outside world (DSL) peaks at only 3.8 Mbits/second, so I would need to set up some kind of LAN server to benchmark network performance in absence of flash-memory or hard-drive writes.

Anybody have any performance numbers to share for:

- OTG mounts of hard drives or SSD devices with NTFS or ext4 file systems

- CIFS/SMB network mounts with CIFS-capable kernels

- WiFi speed tests when remote server is via FiOS or U-Verse fiber connection?

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[Edit] -- Added some network-only test results.

FWIW, I ran a couple of tests using the "netcat" tool to evaluate the same setup without writing files to mass storage devices. It turned out that a terminal emulator app that I have has a busybox with netcat built in, so I booted the WinXp laptop into a Ubuntu Live CD (10.04LTS), and ran netcat TCP write tests in both directions. I also used "iptraf" to look at peak bit rates.

Result? Peak observed speeds were about 16.6 Mbits/second, and sustained-average results were in the 11-12 Mbit/second range. From that I conclude that that the FTP transfer tests were probably network-limited, as testing involving file writes were really no slower than this. Whether that means the "N7 is WiFi limited" or something else is not deducible from the data I collected. In this case, it takes three to tango (N7 - router - laptop).

I do note however that blahman179 said above "100 MB in less than a minute" - 100 MB in 60 seconds is about 14 Mbits/second. Only a little faster than what I observed - right in the same neighborhood.

Note that I had my WiFi router set to G-only. I suppose that the basic bit rate with huge signals in the -30 dBm range means that the radios are indeed transferring packets at a 54 Mbit/sec bit rate - but with a duty factor of less than 30%.