Question about tape backup of online database.

I'd like to know what hardware and software people use to perform tape backup
of an online database on Linux.  I would imagine the following might work(?):

1.	Use RAID mirroring of the disk the db is on onto 2 two or more other
disks.
2.	When it is time to do the backup, disconnect one of the disks from the
mirror and then dump the whole disk partition to a tape(s).
3.	Reconnect the disk back to the mirror and let it begin rebuilding.

Right now, I don't even have SCSI!  If you can tell me your setup and
backup procedure, I'd be grateful.  

 -- 
			Robert