ZFS Severe Performance issue due to poorly supported feature

[Rod Taylor]

I installed ZFS using the 19.10 installer and ran into some severe load caused by /etc/zfs/zed.d/history_event-zfs-list-cacher.sh

Microk8s, due to the way containerd manages container filesystems, causes numerous zevents and can easily overwhelm the above script.

I filed a ticket and partial fix to ZOL team, however in response Richard Elling recommended not using that feature.

* "it is not core to zfs operation, it is an attempt at optimization that few people know about, and even fewer use"
* "zed is allowed to drop events under load, so it might not be called and therefore the cache cannot be authoritative"

https://github.com/zfsonlinux/zfs/issues/9584

I'm providing this feedback to you so you can make changes to the Ubuntu installer to not enable this zfs feature.

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: zfs-zed 0.8.1-1ubuntu14 [modified: usr/lib/zfs-linux/zed.d/history_event-zfs-list-cacher.sh]
ProcVersionSignature: Ubuntu 5.3.0-23.25-generic 5.3.7
Uname: Linux 5.3.0-23-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu8.2
Architecture: amd64
CurrentDesktop: GNOME
Date: Thu Nov 14 10:51:49 2019
InstallationDate: Installed on 2019-10-31 (13 days ago)
InstallationMedia: Ubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
SourcePackage: zfs-linux
UpgradeStatus: No upgrade log present (probably fresh install)

[Colin Ian King (colin-king)]

Refer to the following comment:

https://github.com/openzfs/zfs/issues/9584#issuecomment-554725253

Probably won't disable this feature.