SAP Note 20186 - Online redo log member of a group "INVALID".

Symptom

The status of an online redo log member of a group is "INVALID"
--> DB continues running as long as at least one member of the
group is being accessed --> Status "blank".
This information is contained in table V$LOGFILE

Cause and prerequisites

Access to a member temporarily not available (e.g. hardware problem).

Solution
Once the member can be accessed again, the status will be reset from "Blank" to "File in use" during the next write operation.