[CentOS] Problem with mdadm, raid1 and automatically adds any disk to raid

[Christofer C. Bell]

On Mon, Feb 25, 2019 at 11:54 PM Simon Matter via CentOS <centos at centos.org>
wrote:

> >
> > What makes you think this has *anything* to do with systemd? Bitching
> > about systemd every time you hit a problem isn't helpful.  Don't.
>
> If it's not systemd, who else does it? Can you elaborate, please?
>

I'll wager it's the mdadm.service unit.  You're seeing systemd in the log
because systemd has a unit loaded that's managing your md devices.  The
package mdadm installs these files:

/usr/lib/systemd/system/mdadm.service
/usr/lib/systemd/system/mdmonitor-takeover.service
/usr/lib/systemd/system/mdmonitor.service

Perhaps if you turn off these services, you'll be able to manage your disks
without interference.  I do not use mdadm on my system, I'm just looking at
the content of the rpm file on rpmfind.net.  That said, systemd isn't the
culprit here.  It's doing what it's supposed to (starting a managed service
on demand).

I do concede the logs are confusing.  For example, this appears in my logs:

Feb 26 05:10:03 demeter systemd: Starting This service automatically renews
any certbot certificates found...

While there is no indication in the log, this is being started by:

[cbell at demeter log]$ systemctl status certbot-renew.timer
● certbot-renew.timer - This is the timer to set the schedule for automated
renewals
   Loaded: loaded (/usr/lib/systemd/system/certbot-renew.timer; enabled;
vendor preset: disabled)
   Active: active (waiting) since Thu 2019-02-21 17:54:43 CST; 4 days ago

Warning: Journal has been rotated since unit was started. Log output is
incomplete or unavailable.
[cbell at demeter log]$

And you can see the log message through the service unit using journalctl:

[cbell at demeter log]$ journalctl -u certbot-renew.service | grep "This
service" | tail -1
Feb 26 05:10:07 demeter.home systemd[1]: Started This service automatically
renews any certbot certificates found.
[cbell at demeter log]$

You can see there's no indication in /var/log/messages that it's the
certbot-renewal service (timer) that's logging this.  So it's easy to
misinterpret where the messages are coming from, like your mdadm messages.
Perhaps having the journal indicate which service or timer is logging a
message is a feature request for Lennart!

Hope this helps!

-- 
Chris

"If you wish to make an apple pie from scratch, you must first invent the
Universe." -- Carl Sagan