I've been examining the zfs_arc_max setting to see if this can stabilize the I/O performance. You may like to try setting this as a proportion of your available memory to see if it improves things. For example, with a machine with 8GB of memory, I set this to 2GB and my test system went from being able to reproduce your issue to one where the I/O performance remained constant for hundreds of fio tests.
For example, to set 2GB arc max use: echo 2147483648 | sudo tee /sys/module/zfs/parameters/zfs_arc_max sync echo 3 | sudo tee /proc/sys/vm/drop_caches If it is set too low it impacts on cache hits and this reduces I/O rates. If it is set too high you hit the issue you are seeing because of cache contention between ZFS and the block layer. I suspect the only way to find the sweet spot for your use case is with some careful experimentation. Don't rely on synthetic tests to set this, real world I/O patterns are best to use for this kind of tuning. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1883676 Title: ZFS performance drops suddenly To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/zfs-linux/+bug/1883676/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
