How do I compare the overlap of file sizes between duplicate directories?

I need to compare two directories to validate a backup.

Say my directory looks like this:

Filename        Filesize      Filename        Filesize
user@main_server:~/mydir/     user@backup_server:~/mydir/
file1000.txt    4182410737    file1000.txt    4182410737
file1001.txt    8241410737    -                          <-- missing on backup_server!
...                           ...
file9999.txt    2410418737    file9999.txt    1111111111 <-- size != main_server

      

        
        
        
      

    

Is there a quick one liner that would bring me closer to conclusion, like this:

Invalid Backup Files:
file1001.txt
file9999.txt

      

        
        
        
      

    

(for the purpose of instructing the backup script to update these files)

I have tried getting options for the following to no avail.

[main_server] $ rsync -n ~/mydir/ user@backup_server:~/mydir

      

        
        
        
      

    

I cannot do rsync

to back up the directories themselves because it takes too long (8-24 hours). Instead, I run multiple threads scp

to extract files in batches. This completes regularly <1 h. However, sometimes I find multiple files that have been missed somehow (connection may have been disconnected).

Speed ​​is a priority, so file sizes must be adequate. But I'm open to including checksum

if it doesn't slow down the process as I find with help rsync

.

Here's my test process:

# Generate Large Files (1GB)
for i in {1..100}; do head -c 1073741824 </dev/urandom >foo-$i ; done

# SCP them from src to dest
for i in {1..100}; do ( scp ~/mydir/foo-$i user@backup_server:~/mydir/ & ) ; sleep 0.1 ; done

# Confirm destination has everything from source
# This is the point of the question. I've tried:

rsync -Sa ~/mydir/ user@backup_server:~/mydir
# Way too slow

      

        
        
        
      

    

What do you recommend?