[ILUG] slow ssh compression performance
Paul Mc Auley
paul at novara.ie
Wed Oct 12 08:56:11 IST 2005
On Wed, 12 Oct 2005 08:28:10 +0100 David Malone wrote:
| The suggestion that it may be buffer related is also worth following
| up. If I understand right, The folks that use SSH in a high-performance
| environment have discovered that there buffers inside SSH that have
| the same effect of limiting the TCP window size to some small value,
| which makes it hard to transfer data quickly when the round trip time
| is large. Compression might actually make this a little worse if the
| fixed buffer size is before rather than after compression.
It's also worth considering the fact that the results shown might not be
considered a problem.
A. There is a specific case where I'm able to transfer a lot of empty data
faster by compressing it before handing it to ssh.
B. You should probably do it that way then.
I suspect that if ssh was tweaked to favour large file transfers, its
performance as an interactive shell could be impaired.
As a general rule I tend to prefer to use tar over ssh to transfer
non-trivial numbers of files, I suppose this makes the case for ensuring
that tar adds gzip to the chain too.
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