I just bought an LG BH10LS Blu-Ray burner and was quite "impressed" about the burning time: Although I chose the quite conservative 2x speed it was burning on average with 0.4x which took 4 hours in total! I installed Nerolinux 4 and a Blu-Ray disc takes less than one hour with 2x speed.

which kernel? might be an older one causing it, see https://bbs.archlinux.org/viewtopic.php?pid=759331

remember K3b only calls programs, doesn't actually do the burning, burning usually uses either cdrtools or cdrkit (one's a fork of the other) so you could switch burning programs to see it it make a difference. Also, some session types might use growfs. The k3b log should tell you what command was used to burn.

The kernel is the latest: 2.6.38-3. Distribution is Aptosid.

You mean because of growfs it is that slow?

as I understand it (and I don't have a blu-ray) you could be using 1 of 3 different programs to burn your blu-ray discs and I'm suggesting that by switching programs you might get faster burning speed, also if you know which program is actually being used you can search to see if there's known issues that can be resolved.

I already searched for "slow" and did not find anything in this forum.

the problem with searching just this forum is that the program doing the actual burning is non-KDE, K3b is just a gui wrapper calling growfs, ddrtools or cdrkit to do the actual burning

I know that and you said that already. I consider it a K3B-Problem even though because K3B selects these tools automatically. I know that I can force K3B to use a certain tool and for this reason I would appreciate some competent input and hints.