Hi, I have an iMac and a MacBook Pro. I want to use an external hard drive as a file store, for all my photos and old work. Both the iMac and MacBook Pro will need to access the drive. Is there any problem with two Macs using one drive at the same time? Also I will have a backup of the drive on another external, If I schedule a backup on my iMac (not sure what App. I will use, may set up a RAID 1) will the files still be backed up when I write a file to the drive from my MacBook Pro?