Does A Mirror Array Erase both drives Upon Creation?

I want to create a raid 1 mirror array with two drives. They are both 250gb, one of them has 30gb of data already stored. Upon creation of the array, will the other one catch up and mirror what is already on the other drive? Or is the one drive erased and both start from scratch?

 

This is a classic case of computer theory versus computer reality.

In theory, many RAID drivers allow you to copy an existing drive (RAID 1 has to have this function to rebuild the mirror array if one of the two drives bites it). Check the setup instructions in your motherboard or expansion card documentation to be sure.

In reality, things don't always work out as they should. This is why you should (at the very least) back up all data or (preferably) clone the entire drive before attempting a RAID setup.

Tip: Almost all RAID 1 drivers will let you use different size drives with the RAID capacity being the lesser of the two (example: using both 250GB and a 500GB drive, the RAID capacity will be 250GB).

Ideally, I'd buy a third drive (250-500GB SATA drives are now as low as $39) and clone the data to it before setting up the RAID with the existing drives. Not only is this safer, it gives you a spare drive to immediately rebuild the mirror array if/when one of the RAID 1 drives fails.

One more note: RAID setups normally require both drives to be the same connector type (IDE or SATA).

 

gman, I appreciate the reply. Yeah I figured I should just back up the data to be on the safe side. I have an external drive I'll use. Is there a difference between cloning and just copying the few folders I want to be sure are safe?

 

Copying only backs up specific pictures, documents, etc. It does not back up or copy software or your OS (Windows, MS-Office, etc.).

Cloning makes a mirror image of the drive including Windows, software, etc. (basically what RAID 1 does but without the risk of trashing the data).

If at least one of the drives (either the one with the 30GB of data or the target drive) is a Seagate, you can use Disc Wizard (free), available as a download at Seagate's web site.

 

Generally making a raid setup, would require both drives to be formated to be "setup" in the raid. Once a raid is setup and the drives are matched, then one drive can rebuild the other. But not before that.