I've got a NEC3500A 16x dvd burner and it takes me 14-16 min to burn a 16x DVD. The burning speed is never over 6x but usually 2x-4x. However in the beginning k3b states that the burning speed is going to be 16x. I am running Ubuntu Dapper and have DMA enabled for my DVD drive.

I wonder if it is a Ubuntu specific problem or it is just not possible to have higher speed on Linux in general. Any feedback will be appreciated.

If you are using somekind of buffer underrun protection or similar, it will lower your burn speed if the higher speed would do bad job. You can take this off, but it might cause defective discs. You should also check out K3b's write speed setting -- is it "automatic"? In this case K3b uses the speed it thinks is best for the result; it might vary. You can set this too to be something specific, but again, it might affect the result.

It's not a problem with Linux I think, you should check the other reasons first. That's because I know people who have burned DVDs on higher speeds than 6x.

EDIT: I've experienced with regular writable cds that if one uses very high burn speed, the disc doesn't last as long as a similar disc burned with a lower speed; by this I mean that the high-speed written discs become unreadable (by the same drive I've tried these on) quicker than the low-speed written discs. The result isn't visible right away, but if you store the discs for a long time you should see it. I could think it's exactly the same thing with DVDs, so if you aren't in a hurry and plan to use the disc for a long time, consider using non-maximum speeds. Though if you just use the disc once or twice or overwrite the rw disc soon, it's not that big a matter.