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I am running into severe performance issues using SSH/Rsync on a Synology NAS (model DS413j if anybody knows anything about it).
Both the sshd and the rsync processes are taking 100% CPU on the NAS, and the transfer speed is about 6 or 7MB/s, which is far below the usual network speed -- a Gigabit link that works at more than 50MB/s between other computers on the network. This -- and multiple forum posts about the same kind of issues -- leads me to believe that the bottleneck is the SSH session encryption.
Is there a way to reduce the session key size (or to change to a faster algorithm if necessary)?
F.X.
Posted 2013-08-23T14:21:58.173
Reputation: 111
If it's in a local network you can still switch to the non-encrypted equivalents : FTP, telnet, rsh... At least you can test if your assumption about the encryption being the bottleneck is valid. – mveroone – 2013-08-23T14:30:48.070
I have tested that as well, and the performance is fine, but I want to communicate with an external server, and while cryptography strength is not a huge concern, I'd rather not have things go over the wire completely unencrypted. – F.X. – 2013-08-23T14:44:41.973
You may want to have a look at "High performance SSH patch" : http://www.cyberciti.biz/tips/sshd-server-optimization.html
– mveroone – 2013-08-23T14:54:00.687you can also force the use of the blowfish cipher which is less cpu-intensive :
scp -c blowfich ...(don't know how to specify that with rsync over ssh tho) – mveroone – 2013-08-23T14:56:37.947Remember those NAS have low-speed ARM processors, you may also have reached what your device is capable of... – mveroone – 2013-08-23T15:05:49.847
@Kwaio: Yup, that's what I'm thinking. Blowfish helps a bit, though not by much -- speed is only about 2-3MB/s higher. And I'd rather not installed a patched version... I tried other cipher methods, and nothing better there. – F.X. – 2013-08-23T15:26:31.043
That may be worth a try, the results look promising : http://www.psc.edu/index.php/hpn-ssh
– mveroone – 2013-08-24T11:12:18.290