How to change the number of backups to keep
Otto creates a backup every time it does a migration. Those backups are stored in the _Otto_/Migrations directory inside your Filemaker Server Backups folder. By default Otto saves the last 10 backups. If you have large files this could end up taking up a lot of space.
Changing the Default Number of Backups To Keep
You can do this by setting an Environmental Variable "MIGRATION_BACKUPS_TO_KEEP". These are sort of hidden flags that we can set to allow people to overcome certain issues, like the one noted above.
Setting an Environmental Variable with Otto
Environmental variables are passed to Otto through the use of .env file. This file is placed in the Otto/Config directory.
On Macs this file is invisible. To show invisible files on the Mac, Hold down command + shift and type a period "." It may already be there. If it isn't create it.
On Windows, be very careful to make sure that your file doesn't get created with a .txt extension.
Open or create the file with a text editor place the following on a new line in the file