On Mon, Sep 27, 2021 at 12:00:32PM +0200, Peter Rajnoha wrote: > > - We could use the new lvm-activate-* services to replace the activation > > generator when lvm.conf event_activation=0. This would be done by simply > > not creating the event-activation-on file when event_activation=0. > > ...the issue I see here is around the systemd-udev-settle: Thanks, I have a couple questions about the udev-settle to understand that better, although it seems we may not need it. > - the setup where lvm-activate-vgs*.service are always there (not > generated only on event_activation=0 as it was before with the > original lvm2-activation-*.service) practically means we always > make a dependency on systemd-udev-settle.service, which we shouldn't > do in case we have event_activation=1. Why wouldn't the event_activation=1 case want a dependency on udev-settle? > - If we want to make sure that we run our "non-event-based activation" > after systemd-udev-settle.service, we also need to use > "After=systemd-udev-settle.service" (the "Wants" will only make the > udev settle service executed, but it doesn't order it with respect > to our activation services, so it can happen in parallel - we want > it to happen after the udev settle). So we may not fully benefit from settling unless we use After (although the benefits are uncertain as mentioned below.) > Now the question is whether we really need the systemd-udev-settle at > all, even for that non-event-based lvm activation. The udev-settle is > just to make sure that all the udev processing and udev db content is > complete for all triggered devices. But if we're not reading udev db and > we're OK that those devices might be open in parallel to lvm activation > period (e.g. because there's blkid scan done on disks/PVs), we should be > OK even without that settle. However, we're reading some info from udev db, > right? (like the multipath component state etc.) - Reading the udev db: with the default external_device_info_source=none we no longer ask the udev db for any info about devs. (We now follow that setting strictly, and only ask udev when source=udev.) - Concurrent blkid and activation: I can't find an issue with this (couldn't force any interference with some quick tests.) - I wonder if After=udev-settle could have an incidental but meaningful effect of more PVs being in place before the service runs? I'll try dropping udev-settle in all cases to see how things look. Dave _______________________________________________ linux-lvm mailing list linux-lvm@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
