Biker is correct.
We also use BCVs for something other than a backup for raw disks.
First, we use BCVs to take a snapshot of a production database for backup, but also to use as a Reporting function for our Accounting department. This gives them something to pull reports from the previous days business.
Second, We also use BCVs to copy Databases from one box to another for analysis and development purposes. This is much faster than trying to copy 1/2 a Terabyte or more of data from one box to another. No bandwidth is used up. Of course you need to have Volume groups and Filesystems defined on the second box by BCV with the disk devices that are associated with the Filesystems on the Primary box. Once you have that setup it is simply a matter of making the sync, breaking the mirror and then mounting them on the second box!
BCVs are very useful. You can go to
https://powerlink.emc.com/login/registration.jhtml
There you can download documents that may help.