Enhancing our ZFS support on Ubuntu 19.10 - an introductionn

Now I do run Ubuntu/ZFS from a fast NVME drive (3400/2300 MB/s), I noticed some change. In the past my reboot times of Ubuntu Virtual Machine (VM) from memory cache would be say 12 seconds, Boot times were between 25 and 50 seconds dependent on the fill grade of the SSD cache. Using the NVME drive that difference disappeared, I always boot the VM in 12 seconds, maybe the reboot from L1ARC is 1 second faster.
So it has some consequences for desktop use:

  • I’ll already start reducing the max size of L1ARC, since caching does not really speed up my NVME drive on my Ryzen 3 2200G. While my HDD stored music, videos and spreadsheets, do not require caching
  • Maybe part of the issue is the LZ4 decompression CPU time, maybe we should avoid compression on a NVME drive.
  • Or maybe we should be able to stop caching the content of NVME drives and only cache the drive administration.

Might be worth discriminating between filesystems that are accessed at boot time (no compression) and those that are not (lz4 compression).

True, by default you could keep ROOT uncompressed and only compress USERDATA, when installing on a NVME drive. But I thinks as user, you would like options, finding the optimum balance between CPU speed vs SSD/HDD throughput (R9 + SATA SSD vs R3 + NVME SSD).