Hello, In jessie, the kernel had a very annoying bug: if you did I/O on multiple sr devices, the global lock in sr.c would slow down to a crawl.
E.g. 5 DVD-R written to in parallel gave the same performance as one writing; and ejecting the DVD in parallel was completely sequential. Based on this: https://unix.stackexchange.com/questions/411735/why-does-linux-kernel-driver-sr-c-sr-block-ioctl-do-mutex-lock and this: https://www.spinics.net/lists/linux-scsi/msg63706.html I patched my kernel, and the performance augmented drastically, you can watch the video here: https://www.youtube.com/watch?v=siDMzkRCTpQ&feature=youtu.be or here: https://peertube.gaialabs.ch/videos/watch/7ad190bd-43d9-42dc-9336-984822db7cc3 I even think I reported that bug, but can't find it anymore. However, it seems the kernel used by buster has the same issue. I am now writing with BR drives (two of them) and I get abyssal performance. Anyone can confirm ? I will try to apply a similar patch and possibly report another bug.
