I've got VMWare ESXi (the free version) machine that is booting off a 9650SE RAID-1 drive setup (two 1TB mirrored drives). I'd like to replace the 1TBs with 2TBs.
Is there a safe way to do this?
Yes, this is possible with most hardware RAID controllers. The overview of the steps needed for your controller are here.
You can replace each disk one at a time, allowing time for the drive to rebuild before moving to the next drive.
Once the array is built with the newer, larger disks, you will be able to leverage the additional space at the ESXi level. You can either use it to expand the existing datastore or create a new datastore.
Are you just looking for more space in general, or more space for the existing virtual machines?