SFTP and SCP extremely slow but FTP fast?

FTP client for Android handsets.
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lilledavy
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SFTP and SCP extremely slow but FTP fast?

Post by lilledavy »

I had a very annoying experience when I started to download a large (700 MB) file from my home server to my Galaxy Tab. I used the SFTP and the SCP protocols at first but the download speed never went above 56 KB/s (on a fast server, almost perfect 802.11g network and the galaxy tab more or less ontop of the wireless router).
However, when I gave up and started a proper FTP server instead (vsftp in this case; it's an OpenSuse server) I immediately got download speeds of approx 2000 KB/s.

Why is that? Anyone has a an idea?

Additional info: I tried SCP to the same server from another client (Fedora in this case) at home and then the transfer speed were quite good (13 MB/s), well in line with the network capacity. It doesn't seem to be a misconfigured server.

support
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Re: SFTP and SCP extremely slow but FTP fast?

Post by support »

SFTP is the slowest because of encryption overhead (look at CPU usage it should be high). SCP is quite better and FTP or FTPS is quite fast.

lilledavy
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Re: SFTP and SCP extremely slow but FTP fast?

Post by lilledavy »

Thanks for the overview; makes a lot of sense.

But it doesn't explain the difference I got when using AndFTP:
SFTP, SCP approx 56 KB/s (yes, SCP were slightly faster, a few kB/s)
FTP approx 2000 kB/s. That's almost a factor 40.
Same file, same network (wireless at home), same server.

Is there any network tuning I can do on the Galaxy Tab (Android 2.2) that would affect this?

Imediate update:
After I wrote the stuff above, I checked the CPU-load on the Tab when downloading
1) SFTP (99%), approx 120 kB/s
2) FTP (85%), approx 1800 kB/s
You were quite right all along :-) The decryption is too heavy work for the cpu.
Thanks!

support
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Joined: Sun Apr 20, 2008 4:40 pm

Re: SFTP and SCP extremely slow but FTP fast?

Post by support »

We're trying to find some workaround by allowing lower encryption. But new devices with improved CPU should make it faster.

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