question on DR (Disaster Recovery ) options and tools avaliable

Hi
I am not that familiar with DR tools avaliable . I have used stand by databases and I have one question here -

is there anyway possible that DR database that is the standby database will be kept in open mode along with the main database . someone has told me that it is possible.I am talking about physical standby only.

also what are the different tools avaliable to implement DR at the OS or storage level .what are their main advantages. any pointers to this will be a help.

Regards
Ajeet

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