Need advice on a hard drive upgrade to exchange server.

[mcveigh]

I have a small dell server acting as a file and exchange server for 9 users.

It currently has 3, 18Gb 10k rpm scsi drives in raid 5 (36Gb total)

I want to add at least 18Gb of storage, preferably 36. here are my options:

1) backup everything, add 2 hard drives and reformat the array as raid5 for 72GB of space. then either reinstall from scratch or use backups.
2) add 2 hard drives in a raid 1 array to the existing controller.

I am not used to dynamic disks, could I add the new space to the existing drives using dynamic disks?

thanks!