Please be sure it is working as a NAS and is not shared by the server or another client. Did you install the Drobo software on any client? If so does it spit up any errors? Do the software logs (/Applications/Utilities/Console) spit up any errors while this problem happens? (Please don't post you whole log, just the portion of the error)
Mac Pro Dual 2.8 Quad (2nd gen), 14G Ram, Two DVD-RW Drives, OS X 10.8.3
2006 Mac Book Pro 2.16 (first Gen) OS X 10.7.4
2TB Time Capsule, 2 TB
32G iPhone 4S Black, iPad (3rd Gen) 32G Black
Bookmarks