Writing to DVD-RAM is causing me grief.
For testing I've been using a purpose built Gentoo system, X64, Phenom II CPU (3 cores).
The MB uses the AMD SB700/SB800 AHCI chipset.
I have installed a PCI-e AHCI controller with a JMicron chipset to confirm its not chipset related.
The drive is a new LG model. I've tried a older LG and an old Asus.
Errors are in 2.6.31 and 2.6.32 and almost certainly have been around for a long time.
In brief, if I dd zeros across the entire disk device and if the media is flawless, there are no problems.
If there is a error, dmesg says this
sr 7:0:0:0: [sr0] Unhandled error code
sr 7:0:0:0: [sr0] Result: hostbyte=0x00 driverbyte=0x08
sr 7:0:0:0: [sr0] Sense Key : 0x3 [deferred]
sr 7:0:0:0: [sr0] ASC=0x32 ASCQ=0x0
sr 7:0:0:0: [sr0] CDB: cdb=0x2a: 2a 00 00 1a d0 f8 00 00 02 00
end_request: I/O error, dev sr0, sector 7029728
Buffer I/O error on device sr0, logical block 878716
lost page write due to I/O error on sr0
that /one/ error spawns 22 lines like this
worker  failed while handling '/devices/pci0000:00/0000:00:04.0/0000:02:00.0/host7/target7:0:0/7:0:0:0/block/sr0'
After this one error, the disk cannot be removed with 'eject' (command hangs)
nor can it be formatted or otherwise used.
I reboot at this time.
I would be glad to hear comments on this.