Question: I would like to backup a **single database** residing in a dbspace , while backup utilities in **Informix** such as `onbar` or `ontape` would provide whole system ,logs ,dbspaces backup only .Is there any way to do single database backup in **Informix** ? if there is then please tell me how to *backup* and *restore* a single database ?

Answer: 
If you need backup you could put database in its own dbspace.
Then use "warm restore" only for that dbspace.

If you want to migrate database from instance to instance
you can use dbexport/dbimport or onunload/onload but be careful
and read the manuals first. There are some drawbacks connected with both utilities.
you can use the multitenancy feature if you are running an ids12.10 version. There's a special flag -T to restore a database with onbar in a multitenancy environment.