Neil, Thank you very much. If I chose to write up some documentation on this, where/who might want it? udev documentation in general seems quite weak. Doug On Tue, Nov 1, 2016 at 11:29 PM, NeilBrown <neilb@xxxxxxxx> wrote: > On Wed, Nov 02 2016, Doug Dumitru wrote: > >> Does anyone have any documentation on when a non-root RAID device >> mounts and how this is triggered? >> >> I have dug around looking for calls to 'mdadm' and or references to >> mdadm.conf to read the array details, but am not finding the obvious >> things. Then again, the new boot services still confuses me. >> > > This depends on what the distro you are using chooses to implement. > > If your distro that uses systemd and uses the udev rules and unit files > that are distrubuted with upstream mdadm, then: > > When a device is discovered that contains raid metadata, udev will run > mdadm --incremental --export /dev/whatever > (or similar) > > See /usr/lib/udev/rules.d/64-md-raid-assembly.rules for details. > > Once this has happened for all devices in an array, the array will be > started by mdadm. > > If mdadm notices that the array *could* be started if needed, but that > it still expects more devices to appear, it reports > MD_STARTED=*unsafe* > and the udev rules file uses this to trigger a message to systemd to > start "mdadm-last-resort@devicename.timer" > This sets a timer. When the timer fires, the array is started even > though some devices might be missing. > If the array gets started before that (because the missing devices > appeared) the timer is canceled. > > When an md array (or any other device) appear, some other udev handling, > possibly involving udisks, might cause the filesystem to be mounted. > That is completely outside of the control of mdadm. mdadm just > assembles the device. > > Hope that helps. > > NeilBrown -- Doug Dumitru EasyCo LLC -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
