I just upgraded my empeg (rio) last night with a second drive. I only added a 10 gig, its what was laying around at work. Did it more or less to see how easy it was, in the future I plan to buy and add a much larger drive.
The upgrade was fairly simple. The FAQ on this site was extremely helpful. The hardest thing was getting the hard drive sled out, and back in. It wasn't really that hard to do, but just requred steady hands and patience, I did it really slowly. The descriptions in the FAQ were excellent, there is that can capacitor on the display board, and I could see how many people would accidentally break that.
Building the disk and adding it in was easy. I added a 10 gig hitachi to the 10 gig travelstar already in there, and I had no problems with getting either one to be recognized. The Hitachi is slightly taller than the IBM, but the actual physical disk sizes were reporting being exactly the same when the empeg booted.
All I can say is if you're thinking of upgrading a drive yourself, and you've tinkered with computer parts and electronics before, this is a relatively easy one to pull off. Thanks to tfarbis and others for the excellent faq and linkage. Without the specific warnings and procedures, I would have easily become lost, or more likely broke something.
If you follow the directions, you'll be ok.
BleachLPB
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BleachLPB
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NewFace MK2a