There are many reports that software supplied by a disk vendor, which worked under OS X 10.8 and earlier, can lead to disk corruption after upgrading to 10.9. Many of these reports refer to software from Western Digital. I seem to be suffering from a similar problem with software from Seagate. Seagate offers a driver for use with its Goflex drives. Here is the page where you can download the software: http://www.seagate.com/support/downloads/item/goflex-desk-thunderbolt-master-dl/ Although customer support offered no insight into the problem I encountered, the release notes for this software seem to have been updated to reflect the problem. They state at the bottom: "Supported operating systems: MacOS 10.6.8, 10.7.x, and 10.8.x" It was an unwelcome surprise to update to Mavericks (months after it was released), use disks and installed software as before, then to find that the OS was hanging repeatedly and that my file system has been corrupted. Based on other comments on related issues, I'm inclined to agree with the claim that it is too risky to use any software supplied by a company that supplies hard disks. However, I like many others, also suffered severe data loss using Apple supplied software - iBooks. So I'm also concluding that the Apple ecosphere poses far more serious threats to data integrity than I anticipated. On the narrow problem of reviving the disks, I'm removing all traces of the Seagate software from my macs, working from unaffected backups, and trying to figure out how serious the damage is. I'll update when I know more. I would appreciate any suggestions about how to protect large quantities of data if I continue to work on the Apple platform.