USB Storage Bust
Despite all the attention focused on storage area networks, the dwindling supply of CD-RW drives, and enterprise storage management solutions, I’m still interested in innovative ideas for storage at the desktop. The recent introduction of an 80 GB disk drive for workstations, for instance, naturally generates a whole series of management and user interface questions -- but let’s save that for another column.
As intrigued as I've been by the network area storage (NAS) marketplace, I’ve also been attracted to another clever idea: traditional desktop storage connected via USB. I was so smitten by the idea that I ordered a 16 GB unit with the idea that all my digital photographs, PowerPoint presentations, and MP3 files could have a new home off the system disk. I even thought that a USB disk could act as a new home for application software, taking the load off my traditional system disk.
Installation of my USB unit was as simple as installing the drivers, then, after a quick reboot, connecting the new drive. I started copying JPEGs and MP3s: The unit, while a bit slower than the integrated drive electronics (IDE) drive in my desktop, accepted the files flawlessly. That was as happy as I’d ever be with the unit.
When I first used the drive I connected it directly to the USB port on the back of my computer. To free up a little space for peripherals, I tried connecting it to a simple four-port USB hub. The desktop lost sight of the drive. When I plugged it back into the workstation -- presto! Everything was back to normal.
I reconnected the USB drive directly to my workstation and then had the inspiration to install my copy of Microsoft Office onto the USB drive. The Office Installer is pretty sensitive to long disk write queue. Even though there was no underlying problem with the disk, the Office Installer saw the disk write queue pile up to unacceptable levels. It considers that an unrecoverable error. It proved impossible to successfully get a copy of Office on the drive.
I capitulated, then reinstalled Office onto my system disk. "Maybe it’s just Office," I mused. In the spirit of keeping the system disk from filling up with software the size of the Graf Zeppelin, I tired installing Visio 2000 and PhotoDraw 2000 version 2 on the USB drive. To my surprise both programs installed cleanly -- the first time -- onto the nearly empty USB drive. "I can live with that," I thought as I prepared to take the programs for a test spin in their new locations.
Neither program worked.
While both installed cleanly, neither was able to start up from their new home on the USB attached drive.
Naturally, the USB ports on my machine -- once enabled -- take up a slot on my PCI bus. Indeed, on my machine a separate PCI to USB controller is required to make the disk work. USB’s peak theoretical data rate is 12 Mbps and that seems nimble enough. But every intermediate interface takes its toll on throughput, and a USB drive suffers more than traditional IDE or SCSI drives.
The company that sold me my USB drive claimed that my disk could achieve transfer rates of 8 Mbps and average access times of 10 to 13 milliseconds. Taking all those statistics into consideration it’s no wonder that the USB drive is slower: Access times are 40 percent slower and the transfer rates are pathetic compared to an IDE disk.
The underlying problem appears to be a combination of poor transfer rates and limited buffering. Without substantial read and write buffering, a program like PhotoDraw 2000 is going to have its read queue fill quickly. When the disk is unable to deliver requested blocks and has repeated errors, the underlying operating system reports the problem as a "read error" to the application. In my case the application exited.
Looking into the marketplace, a variety of vendors are selling USB-based disk drives -- some with devices as large as 75 GB. The ease of setup and the emerging ubiquity of USB ports makes USB drives superficially attractive, but remember USB drives can never deliver the performance we see from IDE and SCSI drives. Some software may not even work with USB drives.
If you’re looking for secondary storage that serves limited activity profiles, USB storage may be a useful alternative. If you expect your USB disk to perform as a full partner to an internal drive, you’re likely -- as I was -- to be disappointed. --Mark McFadden is a consultant and is communications director for the Commercial Internet eXchange (Washington). Contact him at firstname.lastname@example.org.