Following up to my own post: Further exploration revealed a couple of things (to me!): The mdcheck_start.timer and mdcheck_continue.timer files under /lib/systemd/system/ contain RandomizedDelaySec settings of 24h and 12h respectively. This appears to be responsible for the odd starting times for the check which is interfering with daytime system use. Why would these values be included for a service intended to only run once a month? I do not want to edit the files under /lib/systemd/system/ which would certainly be overwritten with future updates. Can I place copies of these files in /etc/systemd/system and completely override the entries under /lib/systemd? Clearly, I'm still trying to figure out just how the systemd works and how it integrates with the old legacy init system. On Mon, Apr 5, 2021 at 10:17 AM Jeffery Small <jeff@xxxxxxxx> wrote: > > This is on an Xubuntu 20.04 system. > > I was wondering why I was occasionally seeing a "check" operation > occurring on my clean RAID1 mirrors. Eventually I discovered the > checkarray and mdcheck scripts in /usr/share/mdadm. It appears > that checkarray isn't used (is that correct?), but mdcheck is being > launched by /lib/systemd/system/mdcheck_start.service on the first > Sunday of each month. I have a couple of questions? > > 1: Where do you look for the systemctl scheduling of services > like this? Is there a cron-like scheduler? The time for this needs > to be adjusted. > > 2: Why does mdcheck get a 6 hour run duration set? Right now > it is starting a little after 8 AM, running until 2 PM and then check- > pointed and suspended. On Monday at 9:10 AM it continued due > to /lib/systemd/system/mdcheck_continue.service. It is running on > a 4TB raid that takes over 12 hours to complete, so why stop it > after 6 hours? I'm certainly not getting any advantage to running in > off hours since it is starting at a really inappropriate time. > > 3: The process is really putting a load on the system and interfering > with other work. Can the priority for this process be lowered so that > it doesn't consume so many resources? > > 4: How critical is the check operation? Does it discover things that > the normal RAID operation misses? > > Anything else I should know about all of this? > > Thanks. > -- > Jeffery Small
