What a bag of hurt this has been. On a late 2011 15" MBP with 10.9.1. New Toshiba bare 3T drives (two) in either enclosure here that is compatible with 3T drives, a Seagate GoFLex and an Icy Dock Blizzard. Connect via FW 800. Disk Utility formats and then errors on partitioning. Figured, OK, some of these alerts might be meaningless. Both partitions mount and then error like crazy. Need repair. Repair and repeat. So I hook both drives in combinations of both enclosures to my 2008 MBP with 10.6.8, reformat and run tests with every utility I have including sector check, which returns no errors on anything. Partition into the two partitions I want (a 1T and 2T) and put both, one at a time, back on the Mavericks MBP. Both mount and start erroring again. Mavericks Disk Utility finds problems it cant solve. I boot from recovery partition in case theres something wrong with my system and repeat the first Mavericks formatting procedure. Same results. Cant use them at all. Put them both back on the other MBP at the same time, reformat and partition just for the sake of it and everything works completely fine, all ports. Been running them full blast doing full Tbyte archives for days and theyre fast, quiet, cool. Run utilities from the 10.6.8 MBP on them with perfect results. Nothing wrong. Swap everything everywhere and its the same result. The other drives (up to 2T) that Mavericks liked in the Seagate (which has never hiccuped), among other older enclosures (the rest of mine only go up to 2T so I picked up the Icy Dock) are fine in all the enclosures, including the Icy Dock, on both MBPs. I could find no documentation on Toshiba regarding any Mavericks issues with this mechanism (PH3300U-1172) on any Toshiba page or any forum anywhere, nor with any size Toshiba in other enclosures. No vendor software at all, formatted with Disk Utility every time. Never had anything like this happen on this MBP before updating to 10.9. but consistent results every time I repeat this. Any experiences with Mavericks, even Disk Utility, not liking large drives even when partitioned below 2T? Thanks for any thoughts.