updated readme

README.md

@@ -44,3 +44,19 @@ https://wiki.cpi.imtek.uni-freiburg.de/CPIvServerDocumentation/ElabOnZfs
     rm tmp-backup-file.gz
     ```
 
+
+## notes on implementation ##
+
+At first I tried to implement the complete process in one python file, but this
+lead to an unforseen (and very strange) error:
+
+The created gzip file was not completely written before copying it to the remote
+server. Even closing the file descriptor manually or waiting for a very long
+time would not solve the problem. The gzip was only completed if the python
+process was stopped.
+
+Therefore creating the backups and copying them to the remote server is now a
+two step process, combined in the `run_snapshot_backups.sh` shell script.
+
+I have the idea, that it has todo with the copy on write feature of zfs, but
+I'm not sure about it.