<p>Sanford, You can use Western Digital or Seagate hard drives with your mac. The internal hard drive in your mac is most likely a Seagate drive. There are few things to determine before purchasing your hard drive(s) HD:<br>
1) Are you using Thunderbolt to connect the external drives? Thunderbolt is the fastest way to connect external drives. USB3 is the next fastest. But if your computer is older and doesn't have either ports then getting a faster speed hard drives will not matter.<br>
2) Are these external HDs connected at all times? or you'll have many HDs and continue to swap them as they get full. This will depend on how often you shoot and save files and will need to create a content page so that you can access the specific images.<br>
3) Be careful with the new OS Yosemite. This OS has been causing problems with corrupting external HD. I have two Western Digital drives that got corrupted and can't access anything from the drives.<br>
4) Get a cloud storage service as a backup. incase there is a fire or flood. Your files will be safe. Google Drive or iCloud storage is a great way to go.<br>
In my opinion, 500GB is too small especially shooting RAW and JPEGs. Get 1TB drives and use them as a backup.<br>
I hope this helps you.</p>