Re: How mdadm checks periodically the array in Debian 13 Trixie?

[Andy Smith <andy@strugglers.net>]

Hi,

On Wed, Sep 10, 2025 at 08:55:48PM +0200, Franco Martelli wrote:
> - Which rules "mdadm" now follows to start an array check?

It's done by systemd timers now.

$ systemctl list-units --all mdcheck*
  UNIT                     LOAD   ACTIVE   SUB     DESCRIPTION                      
  mdcheck_continue.service loaded inactive dead    MD array scrubbing - continuation
  mdcheck_start.service    loaded inactive dead    MD array scrubbing               
  mdcheck_continue.timer   loaded inactive dead    MD array scrubbing - continuation
  mdcheck_start.timer      loaded active   waiting MD array scrubbing

As before, the mdcheck_start timer is set to go off on the first Sunday
of the month, but you will see from:

$ systemctl cat mdcheck_start.service

that it is limited to a 6 hour run time, after which it is paused.

The mdcheck_continue timer and service resume the checks at certain
times on following days, until all checks are complete.

> - Is it safe to copy "/etc/cron.d/mdadm" file from Bookworm to Trixie?

There's no need, as your arrays are being checked. If you don't like the
timings you shoul;d probably learn how to change them.

If you do start doing it by cron again then you'll probably want to
disable the relevant system timers. It won't cause harm as the kernel
part of md will just refuse to start a check if one's already running,
but you may end up running checks twice.

Thanks,
Andy

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