OK I found the problem. I always did run the VM without using the Host IO cache, because that ext4 cache might cause an inconsistency during a crash, say one of the 2 to 10 powerfails we have each day in the Caribbean. Besides it is cashing first in the page/ext4 cache and later again in L1ARC.
In 2.4.1 it seem to use direct IO, if you don't use the Host IO cache and direct IO is not cached anymore in L1ARC in 2.4.1. So I enabled all Host IO caches and now L1ARC is filled every 5 seconds with normal writes from the IO cached in the page/ext4 cache. My work has been: The on-line description are very vague. I've reinstalled Ubuntu 24.04 with kernel 6.17 and OpenZFS 2.2. and that worked like expected. The L1ARC was filled fast. Then I installed OpenZFS 2.4.1 on Ubuntu 24.04 and kernel 6.17 and again the L1ARC refused to fill. It did not exceed 0.28 GiB. I went back to Ubuntu 26.04; Kernel 7.0. and OpenZFS 2.4.1 and tried to find a reason why VBox IO did not fill the L1ARC. Somebody mentioned the system uses direct IO, if you do not use the page/ext4 cache on the Host. And direct IO seems to be excluded from L1ARC in 2.4.1. I tried to enable the Host IO cache with 2 - 3 VMs and the L1ARC has now 4.55 GiB. Problem Solved, however these type of serious effects of changes need to be mentioned in the release bulletins of Ubuntu 26.04 and OpenZFS 2.4.1. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2150255 Title: OpenZFS 2.4.1 performance L2ARC collapsed completely To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/zfs-linux/+bug/2150255/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
