Western Digital sent an email to its registered customers over the weekend, warning them not to use their external hard drives on machines that run OS X Mavericks. But the problem seems to go beyond WDD MyBook Studio II external drives; at the very least, the FirmTek eSATA ExpressCard doesn't work properly with Mavericks, and Promise Technology's Pegasus R4-based arrays fall over with Mavericks. Until Apple issues a workaround or patch, it would be very wise to avoid using any external hard drive, or any eSATA- or Thunderbolt-based peripherals, on Mavericks systems.

Word of the problem started circulating early last month, with a post on the Western Digital forum, complaining about lost data on a WD MyBook Studio II. Since then, more than 100 posts on a dozen different threads repeated the observation that upgrading to Mavericks leads to lost data on the WD MyBook Studio II.

Western Digital responded with an email last Friday that says, in part:

As a valued WD customer we want to make you aware of new reports of Western Digital and other external HDD products experiencing data loss when updating to Apple's OS X Mavericks (10.9). WD is urgently investigating these reports and the possible connection to the WD Drive Manager, WD Raid Manager, and WD SmartWare software applications. Until the issue is understood and the cause identified, WD strongly urges our customers to uninstall these software applications before updating to OS X Mavericks (10.9), or delay upgrading. If you have already upgraded to Mavericks, WD recommends that you remove these applications and restart your computer. The WD Drive Manager, WD Raid Manager, and WD SmartWare software applications are not new and have been available from WD for many years, however solely as a precaution WD has removed these applications from our website as we investigate this issue.

That generic advice from WD was updated with additional recommendations, on Nov. 1:

If you have already upgraded to Mavericks and are experiencing difficulty in accessing your external hard drive, please do not save anything to the drive, disconnect the drive from your computer, and contact Western Digital Customer Service at http://support.wdc.com/country/ for further assistance.

A WD Tech Support staff member has just published these detailed instructions:

Run the SmartWare uninstaller application located in /Applications/ Using Apple's Activity Monitor from /Applications/Utilities quit the following processes: WDDMService WD Quick View SmartwareServerApp Delete /Library/LaunchDeamons/com.wdc.WDDMService.plist (Entry that causes WDDM to start.) Delete /Library/LaunchDeamons/com.wdc.WDSmartWareServer.plist (Entry that causes the SmartWare Server to start.) Delete /Applications Support/WDSmartware (Removes all SmartWare support programs) Delete /Application/WDSmartWare (SmartWare user interface) Delete Library/Preferences/com.wdc.smartware.plist From System Preferences->Users Login Items remove WDQuickview for all users. (Entry that runs WD Quick View when a user logs in. There should be a single entry for all users. Deleting it from one any account should remove it for all accounts.)

Following those instructions will take out WD SmartWare, and at that point you will be able to access the drive, without fear of destroying data. It isn't clear at this point if Apple and/or Western Digital will be able to get your data back. It also isn't apparent why WD failed to test sufficiently to avoid this problem before it was released to the masses. Finally, it isn't known if (as the WD email asserts) other external hard drives, from whatever manufacturer, are having the same problem.

Apple support forums look like vicious mud-slinging arenas (what else is new?), but knowledgeable speculation at this point focuses on the possibility that the SATA bridge firmware card inside the WD MyBook isn't cooperating with Mavericks. David Morgenstern at ZDNet too reports on several additional, probably related, problems.

For starters, many eSATA ExpressCard are having problems, specifically on the 17-inch, mid-2010 MacBook Pro, when it's upgraded to Mavericks. The Apple Support community has customer complaints about the LaCie eSATA/USB 2in1 ExpressCard, the Griffin eSATA ExpressCard, the Seritek 2SM2-E adaptor, the generic JB Micron adapter, a Lacie eSATA 2 port ExpressCard, the Sonnet Tech Tempo SATA ExpressCard/34, the Merax eSATA ExpressCard, the Best Connectivity ExpressCARD/34mm, the FirmTek eSATA ExpressCard, and more. Several posts on the Apple forum give various suggestions for installing older drivers that may or may not work. Apparently, this is only an issue with the 17-inch, mid-2010 MacBook Pro.

In addtion, the Promise Thunderbolt Pegasus R4 has encountered several problems that appear to be Mavericks-related.

If you're having eSATA- and/or hard drive-related problems with Mavericks, please post details in the comments. We'll run a follow-up story in Tech Watch as soon as more details filter in. (Add a comment.)

This article, "OS X Mavericks upgrade destroys data, reports Western Digital," was originally published at InfoWorld.com. Get the first word on what the important tech news really means with the InfoWorld Tech Watch blog. For the latest business technology news, follow InfoWorld.com on Twitter.