Running multiple scp threads simultaneously

Question

Running multiple scp threads simultaneously:

Background:

I'm often finding myself mirroring a set of server files a lot, and included in these server files are thousands of little 1kb-3kb files. All the servers are connected to 1Gbps ports, generally spread out in a variety of data-centers.

Problem:

SCP transfers these little files, ONE by ONE, and it takes ages, and I feel like I'm wasting the beautiful network resources I have.

Solution?:

I had an idea; Creating a script, which divides the files up into equal amounts, and starts up 5-6 scp threads, which theoretically would then get done 5-6 times faster, no? But I don't have any linux scripting experience!

Question(s):

• Is there a better solution to the mentioned problem?
• Is there something like this that exists already?
• If not, is there someone who would give me a start, or help me out?
• If not to 2, or 3, where would be a good place to start looking to learn linux scripting? Like bash, or other.

Solution 1

I would do it like this:
tar -cf - /manyfiles | ssh dest.server 'tar -xf - -C /manyfiles'

Depending on the files you are transferring it can make sense to enable compression in the tar commands:
tar -czf - /manyfiles | ssh dest.server 'tar -xzf - -C /manyfiles'

It may also make sense that you choose a CPU friendlier cipher for the ssh command (like arcfour): tar -cf - /manyfiles | ssh -c arcfour dest.server 'tar -xf - -C /manyfiles'

Or combine both of them, but it really depends on what your bottleneck is.
Obviously rsync will be a lot faster if you are doing incremental syncs.

Solution 2

Use rsync instead of scp. You can use rsync over ssh as easily as scp, and it supports "pipelining of file transfers to minimize latency costs".

One tip: If the data is compressible, enable compression. If it's not, disable it.

Solution 3

Not scp directly, but an option for mutli threaded transfer (even on single files) is bbcp - https://www2.cisl.ucar.edu/resources/storage-and-file-systems/bbcp.

use the -s option for the number of threads you want transferring data. Great for high bandwidth but laggy connections, as lag limits the TCP window size per thread.

Solution 4

I was about to suggest GNO Parallel (which still requires some scripting work on your part), but then I found pscp (which is part of pssh). That may just fit your need.

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Comments

[Scott Pack]

possible duplicate of How to copy a large number of files quickly between two servers

[David Schwartz]

It seems pssh operates concurrently to multiple machines. I don't think it implements file-level parallelism.

[Rilindo]

I probably should be specific - I meant pscp.

[aendra]

I just did one transfer last night with scp and am doing another similar transfer with rsync -- it seems a lot faster. However, it still seems to be transferring one file at a time — any idea how to make this do multiple threads (Beyond --include'ing and --exclude'ing a bunch of directories via script; see: sun3.org/archives/280)

[Joe]

There's no point transferring multiple files at the same time given the limited bandwidth. I believe you won't consider this command when the bandwidth is abundant. Eliminating the latency cost already helped a lot when you are coping a lot of small files. Even if you can copy multiple files at the same time, the limited bandwidth won't speed up your file transfer.