Update shell-and-data-access.md

docs.it4i/general/shell-and-data-access.md

@@ -161,9 +161,9 @@ local $ rsync -r my-local-dir username@cluster-name.it4i.cz:directory
 
 !!! note
     The data transfer speed is limited by the single-core ssh encryption speed to about **150 MB/s**  
-    Use **parallel rsync** for unlimited transfers
+    Run **multiple rsync** instances for unlimited transfers
 
-The parallel rsync transfers multiple files at the time, utilizing multiple rsync processes and cores to accelerate encryption.  
+Parallel execution of multiple rsync processes utilizes multiple cores to accelerate encryption and multiple tcp streams for enhanced bandwidth.  
 First, set up ssh-agent single sign on:
 
 ```console
@@ -172,14 +172,14 @@ local $ ssh-add
 Enter passphrase for /home/user/.ssh/id_rsa:
 ```
 
-Then run the rsync in parallel:
+Then run multiple rsync instances in parallel, f.x.:
 
 ```console
 local $ cd my-local-dir
-local $ ls | xargs -I% -n 1 -P 4 rsync % username@cluster-name.it4i.cz:my-remote-dir/.
+local $ ls | xargs -n 2 -P 4 /bin/bash -c 'rsync "$@" username@cluster-name.it4i.cz:mydir' sh
 ```
 
-The -P YYY argument determines number of parallel rsync processes. Set to number of cores on your local machine.
+The -n XXX argument detemines the number of files to transfer in one rsync call. Set according to file size and count. The -P YYY argument determines number of parallel rsync processes. Set to number of cores on your local machine.
 
 On Windows, use the [WinSCP client][c] to transfer data. The [win-sshfs client][d] provides a way to mount the cluster filesystems directly as an external disc.