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For a while now, my trusty 20gb iPod Photo has been having uncharacteristically weird problems syncing with iTunes. It would often stop syncing with the error "Disk cannot be read from or written to". Finally, it got so bad that it hardly sync'd any files at all. Looking in the Mac OS Console utility (/Applications/Utilites/Console.app), I finally noticed everytime this happened, the Mac would report "data underrun" errors.

So at this point, I thought perhaps it was a corrupted iPod hard drive. I tried restoring my iPod a few times, even completely erased the parition at one point using Disk Utility. I even tried an anecdotal method that requires that you change your Mac's timezone to PST, restore the iPod and then revert your timezone. But the iPod still had the same problem syncing.

Then I came across some forum postings that mention that iTunes will choke on the syncing, if the file it's trying to copy is not readable by iTunes. I checked all my file permissions but they were all fine (readable/writeable by my user on the Mac), so that was a dead end.

Then I found some sites that mentions the iPod's hidden diagnostic menus. Running the iPod diagnostics helped point me in the right direction. I ran all the iPod hard drive tests and they all said it was OK. So I figured that the drive was probably still okay. I also tried my own crude write tests to the iPod drive:

$ cd /Volumes/iPod
$ mkfile 5g 5gig.file

"mkfile" is a UNIX level command that let's you create a file of a given size easily. I was able to create pretty much any size file on the iPod without any errors. So at this point, I figure it's maybe an OS or application level issue.

Now so far, I had been plugging my iPod into the front USB port of my PowerMac G5 everytime. I figured that was the simplest setup, no hubs or other intermediary devices that could potentially interfere with the syncing. I hadn't really tried a different USB port yet, assuming that surely the built-in USB port was fine. So finally I decided to rule out the USB port on the computer by plugging the iPod into the USB port on my monitor (which was in turn connected to a hub and then into the back of the G5).

Wouldn't you know it. Syncing worked 100% after that. No errors, no underruns, no problems. Syncs gigs of files with out a single complaint.

So in the end, it was a basic hardware issue. What lulled me was that the front USB port does not have problems with other USB devices, although perhaps it will start to later on. So possibly it's the way the iPod USB cable seats into the USB port, or some combination of things.

In any case, I was just glad to have figured it out, and without having to try any surgery on the iPod or pay for a repair.

Just for reference here are some resources I came across to while trying to fix my iPod issue:

• Apple's knowledge base entry for iPod troubleshooting
• Enabling your iPod's diagnostic mode to test everything from power, the connectors, the LCD screen, the hard drive, the sound, and more.
• Handy visual chart of iPod sequences for reset/reboot, diagnostic mode, disk mode.

Apparently some types of iPod issues (sad iPod icon) sometimes benefit from some "tough love" (i.e., smack it). Or you can open up the iPod and do your own fix-it (replace the hard drive, or reseat the connectors).