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  1. scp user@aws-ec2:~/file file
  2. rsync --partial --progress -Pav -e ssh user@aws-ec2:~/file file

scp only gives me 200K/s, but rsync gives me 1.9M/s

I tested several times, all same results.

rsync uses multiple threads??

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2 Answers 2

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9

Both of the protocols are based on SSH. And SSH itself has some overhead: wiki

SCP is really naive protocol with really naive algorithm for transferring a few of small files. It has a lot of synchronization (RTT - Round Trip Time) and small buffers (basically 2048 B -- source).

Rsync is made for performance and therefore it gives much better results and have more features.

The 10x speedup is specific for your case. If you would transfer files over the whole world over high-latency lanes, you would get much worse performance on the scp case, but on local network, the performance can be almost the same.

And no, compression (-C for scp) will not help. The biggest problems are the latency and buffer size.

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8

RSYNC vs SCP

SCP basically does a plain old copy from source to destination locally or across a network using SSH but you may be able to use the -C switch to enable SSH compression to potentially speed up the copy of data across the network.

RSYNC transfers just the differences between two sets of files across the network connection, using an efficient checksum-search algorithm that automatically optimizes the network connection during a data transfer.

RSYNC

DESCRIPTION

   rsync is a program that behaves in much the same way that rcp does, but
   has many more options and uses  the  rsync  remote-update  protocol  to
   greatly  speed  up  file  transfers  when the destination file is being
   updated.

   The rsync remote-update protocol allows rsync to transfer just the dif-
   ferences between two sets of files across the network connection, using
   an efficient  checksum-search  algorithm  described  in  the  technical
   report that accompanies this package.

source

SCP

DESCRIPTION

 scp copies files between hosts on a network.  It uses ssh(1) for data
 transfer, and uses the same authentication and provides the same secu‐
 rity as ssh(1).  scp will ask for passwords or passphrases if they are
 needed for authentication.




 File names may contain a user and host specification to indicate that
 the file is to be copied to/from that host.  Local file names can be
 made explicit using absolute or relative pathnames to avoid scp treat‐
 ing file names containing ‘:’ as host specifiers.  Copies between two
 remote hosts are also permitted.

source

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  • 3
    In this case, the situation is a bit different though: He’s only copying a single file. (That presumably doesn’t exist yet on the remote end.)
    – Daniel B
    Commented Jul 15, 2016 at 6:19
  • 1
    @DanielB You don't think it could still be that RSYNC by default optimizes the data connection even for the one file and perhaps compressing the data during the transmission so less data chunks are actually sent down the pipe whereas the SCP without the -C switch doesn't compress data during the transmission of it down the pipe?
    – Vomit IT - Chunky Mess Style
    Commented Jul 15, 2016 at 6:41
  • 2
    Neither compression nor checksumming are specified in his rsync command line. Of course the in-file delta algorithm is always active. It’s probably just that scp sucks.
    – Daniel B
    Commented Jul 15, 2016 at 7:08

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