Currently the admins that want to look at the datafile usage of a particualr target are having to enter the username and password everytime for the database. The save option or checkbox is disabled where as the sysman account can save credentials.
One way out of this that i found is create a named credential for a particular database target and grant this credential view privilege to the admin who wants to access the db. After this is done when the admin clicks on datafiles option of the database in OEM it shows him the saved credentials that i granted him so he does not have to enter any credentials. My question is is this the right way to do it? bcos there are hundreds of databases and if the dba does not want to enter the credentials everytime he wants to check the datafile usage or any admin task, would i have to create the named credentials for all these databases and grant them to the dbas? Also why is the save check box disabled for the dba to save the credentials by himself?
If the user/pwd is the same, the best option is to create the named cred as you did, then store that as the Preferred Credential for database targets (Setup -> Security -> Preferred Credentials). This will be used as the default login and only prompt if the acct/pwd doesn't work. The most likely reason for the save being disabled, is that there's a privilege for Named Credentials, so you can try granting that to the user and see if he can then create/modify his own credentials.
Just go under Setup --> Security --> Named Credentials. Any admin should be able to create a named credential. By making the credential scope 'Global', you can then grant access to this credential to other users.