after 10.1.3, MO removable no longer writeable...

Hate to say it, but I think you're experiencing the OS X equivalent of an extension conflict. Looking at modification dates you might want to ask Apple/Fujitsu to check the AppleStorageDrivers.kext kernel extension package and probably AppleATAPIStorage.kext in particular. It's part of the above driver package and appears to have been revved in 10.1.3. It looks like 7 other drivers in this package were revved too, but thay don't look like culprits here.

Good luck! I bet if you get a solution to this you may make some DVD-RAM owners happy too.

I'm experiencing the same problem too with my USB Flash Drive, PenDrive.

I use the drive on a daily basis, and have spent the whole of yesterday re-installing OS X since there's no easy way to downgrade back to 10.1.2. Argh!

I should mention that the drive works nicely (up to 10.1.2) without needing its own driver. Hence, an extension conflict mentioned by Craig seems unlikely in this case.

Does anyone know how I can report this problem to Apple?

in a similar thread I started elsewhere, other people are reporting the exact same nowrite situation with other storage devices. (Apacer HandyDrive)

luckily I kept a 10.1.2 partition, and have migrated back there until there is a resolution to this. Of course, in 10.1.2 I can use my MO drive perfectly normally.

I'm on hold with 1-800-SOS-apple right now, but the problem will be that since I installed the dynaMO drive myself, its unlikely they'll help or offer anything in the way of support.

UPDATE: got off the phone from the apple number. As I suspected, they offered me nothing in way of support (they weren't obligated to) and the guy basically laughed and said "I'll make a note of it". I had to explain to him over and over what the fujitsu drive actually was. Even in the end he kept referring to it as a "cdrw". When I corrected him that it was an MO disk, he had NO idea what an MO disk was. (he still didnt, even after I explained it, he thought I meant a static rather than removable optical drive). I don't hold out much hope for this situation. Therefore, I must remain at 10.1.2

Have you tried replacing the 10.1.3 copy of "AppleStorageDrivers.kext" with the one from your working 10.1.2 partition? Back up the newer one first, of course. It lives in /System/Library/Extensions.

It sounds like since the 10.1.3 partition doesn't work for you anyway, and you have a fallback to 10.1.2, there's not much risk in trying.

unfortunately, I tried it and it doesn't work.

I have a SCSI Fujitsu Dynamo 640 plugged into an Adaptec 2930 card on my B&W G3 OS X 10.1.3. I think I did have some trouble with one disk that I had to reformat, but otherwise seems to be writing ok.

after not hearing I finally called Fujitsu. They not only replicated my problem, they are flat out saying Apple screwed up and will fix it in 10.1.4.
Their advice is to stay at 10.1.2 (which I am doing anyways).

so, I'm not just nuts. (well, I probably am, but NOT for this reason.)

I encountered pretty much the same problem with my PenDrive (a USB Flash Memory storage device) after upgrading to 10.1.3. PenDrive did acknowleged the problem and delivered a patch about 2 weeks ago to resolve it.

What I discovered while I was waiting for the patch from PenDrive is that SmartDisk's various USB storage devices also have the same problem. SmartDisk has also made available a patch to resolve it. Out of curiosity, I downloaded the patch (http://www.smartdisk.com/downloads.asp) from SmartDisk and compared it to PenDrive's patch (http://www.pendrive.com) . I found out they are pretty much the SAME patch.

I now believe it really is Apple that screwed up. Afterall, the PenDrive and SmartDisk's various storage devices are entirely different products. They do, however, share the same underlying tech; USB mass storage class devices.

I'm quite disappointed with Apple in this matter. It wasn't long ago in the 10.1.1 upgrade that Apple screwed up and my Oxford 911 firewire drive refused to mount.

(BTW, the said patch doesn't work for me, although I've read that it works for others. Argh!)

10.1.4 update does NOT fix this problem.