On 6/30/20 11:42 AM, Zdenek Kabelac wrote:
Dne 30. 06. 20 v 11:34 Vitaly Zaitsev via devel napsal(a):
On 30.06.2020 11:23, Igor Raits wrote:
Sadly you can't have lvm2 not installed:

Yes, but it can be disabled.

Of course, you can disable this yourself if you are skilled admin and you do 
not need it or use it (you can mask it which is even better).

Default for unskilled users who may use lvm2  - should remain enabled.

So I just did some research on this and the lvm2-monitor.service name is 
misleading. This service starts dmeventd (through lvm commands) and on most 
lvm setups, as we create them with anaconda's default auto-partitioning dmeventd
is not necessary at all. Actually I use the auto-partitioning on all my systems
and I always disable lvm2-monitor.service without any bad side-effects.

man dmeventd helps a lot here, dmeventd monitors events on devices used by
device-mapper and acts on them through plugins the following plugins are
available (see man dmeventd and then the "LVM PLUGINS" section) :

mirrorring/raid -> In this case dmeventd attempts to handle device failure,
this is definitely good to have but only if mirroring/raid is used,
which in practice means that dmraid is used.

snapshot/thin/vdo -> dmeventd monitors if the storage pool is running out
of space and if it is it sends a warning to syslog. This maybe is somewhat
useful but only in combination with another monitoring system monitoring
syslog for these messages and pro-actively contacting the admin; and this
is only relevant if snapshot/thin/vdo lvm features are used, which in a
default Fedora install they are not.

So this is a third case (next to dmraid and device-mapper-multipath) of
a device-mapper/lvm related service which is always starting itself
(taking time and resources) needlessly on 99.9% of all Fedora workstation

I really wish that the lvm/device-mapper team would pay more attention
to this. As Lennart mentioned in the thread, the dmraid issue has been
a known issue for 10 years now and dmraid really need to be changed to
be activated based on blkid results rather then always start and scan
all disks.

My proposal for now for the lvm2-monitor.service is to change the
Workstation pre`set to disabled and to make dmraid-activation.service
have a Requires= on it.

This way for dmraid setups we keep the code attempting to deal with

As for snapshot/thin/vdo we do not use that by default in Fedora workstation
and as mentioned logging a warning to syslog is not all that useful anyways
unless additional manual setup is done to automatically monitor syslog for
this, in which case enabling the service is just a tiny extra step when
already manually setting up the monitoring.


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