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Speed issue with SSH/Unison on SuSE9.2

 
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photobod



Joined: Thu Apr 21, 2005 8:18 pm
Posts: 94
Location: London

PostPosted: Mon May 30, 2005 10:37 pm    Post subject: Speed issue with SSH/Unison on SuSE9.2 Reply with quote

I'm trying to set up Unison to sync backups on a small LAN. It all works fine, except that the transfer rate is very slow compared to the normal speed of the LAN.

The PC's are both using Unison on SuSE 9.2, connected by SSH. I'm getting about 80KB/sec on a 100Mb/sec LAN that normally manages about 10MB/sec over NFS.

Is the lack of speed due to ssh or to Unison? Is there any way to tweak whichever is causing the slowdown to improve matters?

Thanks,

Neil Lewis
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Rhakios
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Joined: Thu Apr 07, 2005 12:18 am
Posts: 7604
Location: Midlands, UK

PostPosted: Mon May 30, 2005 10:41 pm    Post subject: RE: Speed issue with SSH/Unison on SuSE9.2 Reply with quote

ssh can slow things down, especially on older hardware due to the encryption overhead, but even so I can get 4MB/sec out of a 600MHz Celeron. So, I expect it's the Unison part of the set up.
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photobod



Joined: Thu Apr 21, 2005 8:18 pm
Posts: 94
Location: London

PostPosted: Mon May 30, 2005 10:45 pm    Post subject: RE: Speed issue with SSH/Unison on SuSE9.2 Reply with quote

Thanks Rhakios. At least I can now concentrate on Unison as the cause of the problem.
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nelz
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Joined: Mon Apr 04, 2005 12:52 pm
Posts: 8368
Location: Warrington, UK

PostPosted: Mon May 30, 2005 11:20 pm    Post subject: RE: Speed issue with SSH/Unison on SuSE9.2 Reply with quote

I've just tried a Unison sync and got around 3MB/s. That was transferring a lot of small mail files, where you would expect overhead to be a problem. With a single large compressed file, I get around 1.3MB/s, so Unison is certainly capable of more than 80KB/s.

You can reduce the SSH overhead by switching to a less CPU-intensive cipher. I have set the default to blowfish, by adding "Cipher blowfish" to /etc/ssh/ssh_config on both machines.
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photobod



Joined: Thu Apr 21, 2005 8:18 pm
Posts: 94
Location: London

PostPosted: Wed Jun 01, 2005 10:58 pm    Post subject: RE: Speed issue with SSH/Unison on SuSE9.2 Reply with quote

That's very useful info, thanks Nelz.
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