I have two external USB/Firewire hard drive enclosures that I use for backup and offline storage. They're indispensible, especially when I'm dealing with a notebook computer or a mini-micro-tiny-tower that doesn't let you install a new drive internally.
But these drive enclosures have their fair share of pitfalls, including bad ribbon cables and faulty USB connectors. Not to mention the problem I ran into when migrating 50GB of data from an external drive to an internal one.
External drives use a "bridge" device—a controller that converts the IDE (PATA) or SATA signals from the drive to something that can be sent over the USB bus. Normally the bridge controller works fine ferrying messsages between both types of buses, but if there's a CRC error on the drive, it may not be reported back to the host the same way a locally mounted drive would.
While I was migrating the 50GB of data, the copying process seemed to go to sleep about halfway through; after a certain point, there was absolutely zero disk activity. I quit the copy action, then retried it from the console via < a href=http://searchwincomputing.techtarget.com/tip/0,289483,sid68_gci1248206,00.html>Robocopy (I'd done it in Windows Explorer, basically because I was lazy) and watched the whole thing unfold. When a certain file was reached, the copy operation stopped hard.
Time for a different tactic. I disconnected my DVD drive to free up an IDE socket, then took the external drive out of its cage and mounted it in my PC. When I retried the copy operation with the drive running internally, it threw a CRC error with that file and died. In the end, about three files out of the 50GB batch were bad and couldn't be copied. Fortunately, none of them were irreplaceable, so I was spared the possibility of calling a data recovery clinic and begging them on bended knee for assistance.
I'm still trying to figure out if the problem is due to the bridge controller, or if it's a shortcoming in the way Windows handles external USB storage devices. My guess is the problem is due to the controller in question -- the drive cage only cost me $30, and I suspect in this case I got what I paid for. But my mind remains open to the possibility that this is a Windows issue.
About the author: Serdar Yegulalp is editor of the Windows Insight, (formerly the Windows Power Users Newsletter), a blog site devoted to hints, tips, tricks and news for users and administrators of Windows NT, Windows 2000, Windows XP, Windows Server 2003 and Vista. He has more than 12 years of Windows experience under his belt, and contributes regularly to SearchWinComputing.com and SearchSQLServer.com.
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