[SOLVED] unison over ssh: was it faster before?

Xyne · 2013-11-30 17:55:33

I use unison over ssh to sync a laptop and a desktop on a gigibit cabled LAN. Until recently I'm almost sure that I was getting great speeds while syncing (~80+ MB/s) but now I only seem to get ~5 MB/s and the difference is irksome.

The connection itself seems fine because pacserve is still able to pass around packages at 80+ MB/s between the systems. I ran the long tests with smartctl to check the disks on both as well but no errors were reported.

Does anyone have any debugging suggestions? I would also like to know what speeds others get and if anyone has noticed a change in the last few weeks.

Last edited by Xyne (2013-12-16 02:42:18)

mrinx · 2013-11-30 18:13:31

Maybe I'll sound dumb, but I think 5 MBps over ssh is a really nice speed. I think ssh is slower in general, because it's doing some encryption on the fly, so it's slow no matter how fast is your network (at least I live under that impression).

WonderWoofy · 2013-11-30 20:24:17

mrinx wrote:

Maybe I'll sound dumb, but I think 5 MBps over ssh is a really nice speed. I think ssh is slower in general, because it's doing some encryption on the fly, so it's slow no matter how fast is your network (at least I live under that impression).

No this doesn't sound dumb. I think that is about what I get when SSH'ing over LAN as well. I was able to make it slightly faster by using the HPN patchset, but it wasn't much since I am able to use the aes-intel module for it anyway.

@Xyne, have you tried downgrading the unison packages on both machines just to see if it is indeed unison itself?

mrinx · 2013-11-30 20:31:41

Yeah, I did some small research for myself, there should be a possibility to make an ssh faster by using different cipher and maybe not using compression. I guess it's best to do some testing on your own configuration and see what would be the fastest method.

WonderWoofy · 2013-11-30 21:37:34

On modern processors, there is hardware crypto functionality. So with newer machines at least, using aes should be the fastest, since that is compatible. But if you use the High Performance Networking patchset, you can have it multi-threaded or even set it up to have no encryption (hopefully one would only use this in a secure LAN setting).

Link to SSH-HPN. The only problem with that patchset is that it typically lags behind the Arch repo's openssh package by one release. So when there are vital security fixes in the package, it doesn't make much sense to stick with it.

But that is all a bit OT from Xyne's original intent of this thread.

defears · 2013-11-30 22:09:22

I had 2 1G network desktops at one point (gave one away) and noticed a couple of things while I had that setup

Both desktops in performance mode with no encryption, transfering a 2 Gig movie file. 120MBs
If one was using ondemand. 100MBs
If both were using ondemand. 80MBs
Both using ondemand and encryption. 50MBs
Both using ondemand, encryption, checksums and big files. 25MBs
Both using ondemand, encryption, checksums and thousands of small documents I would be lucky to hit 10MBs.

Xyne · 2013-12-16 02:55:09

Thanks for the replies.

While syncing today I saw sustained speeds of 80-100 MB/s. I have not changed my unison or ssh(d) configurations so I suspect that this was a transient error in some package.

Incidentally, when I was testing this I created large files with dd from /dev/urandom and made sure that they were the only files being transferred to rule out problems due to the number of files. Today I tested the speed with different cpu governors. There may have been a slight increase at the beginning but I did not notice anything after that.

To summarize, I am now getting transfer speeds of 80-100 MB/s with unison over ssh, using 4096-bit public key authentication and the default compression setting (delayed). My default cpu governors are powersave (laptop) and ondemand (desktop). Changing to performance on both does not seem to have a significant effect.

I still don't know what happened, but I'm happy, so I'm marking this as solved.

Arch Linux

#1 2013-11-30 17:55:33

[SOLVED] unison over ssh: was it faster before?

#2 2013-11-30 18:13:31

Re: [SOLVED] unison over ssh: was it faster before?

#3 2013-11-30 20:24:17

Re: [SOLVED] unison over ssh: was it faster before?

#4 2013-11-30 20:31:41

Re: [SOLVED] unison over ssh: was it faster before?

#5 2013-11-30 21:37:34

Re: [SOLVED] unison over ssh: was it faster before?

#6 2013-11-30 22:09:22

Re: [SOLVED] unison over ssh: was it faster before?

#7 2013-12-16 02:55:09

Re: [SOLVED] unison over ssh: was it faster before?

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