Thanks for explaining this! regards, Martin On Fri, Mar 7, 2014 at 8:13 PM, Joe Landman <joe.landman@xxxxxxxxx> wrote: > On 03/07/2014 03:00 PM, Chris Murphy wrote: >> >> >> On Mar 6, 2014, at 7:13 PM, Martin T <m4rtntns@xxxxxxxxx> wrote: >> >>> Hi, >>> >>> while most of the Linux software-RAID related tutorials suggest to >>> have the mdadm.conf file up to date, then is it actually needed or >>> used any more? I mean all the data needed by kernel for creating >>> the RAID arrays should be stored in the superblocks, shouldn't it? >>> Or in which situation the mdadm.conf is needed? >> >> >> Good question. mdadm.conf is baked into the initramfs by dracut, >> along with mdadm, on Fedora systems. I haven't tried to willfully >> break it by deleting mdadm.conf and rebuilding the initramfs to see >> if it still works. > > > On diskless systems, I have as part of the startup, an > > mdadm --examine --scan > /tmp/mdadm.scanned.conf > mdadm -As --conf=/tmp/mdadm.scanned.conf > > so technically its not needed a-priori here. For systems with the root on a > particular RAID you would want to assemble the RAID before the switch. Most > dracut based systems complain quite vociferously when you make mdadm go > away, as they don't seem able to do what we've done above to figure out what > they should assemble. > > >> I'm pretty sure it happens within the initramfs prior to the kernel >> even attempting to mount root. On systemd systems this could be >> better learned by passing systemd.log_level=debug >> systemd.log_target=console. The initramfs contains systemd, mdadm, >> mdadm.conf - and I'm pretty sure systemd activates that service, and >> then mdadm uses the mdadm.conf that's in the initramfs to assemble >> the array, and then systemd mounts it per the kernel command line >> which specifies root as an mduuid. > > > It would be nice if, as part of the startup, it did a scan, a comparison of > the root device to whats available, and instead of timing out or panicing > (both of which I've seen), that it drops into a shell if the root raid > device is either a) not there, or b) not ok to assemble. The rd.shell > dracut line sorta/kinda does this. I am not sure what the systemd > equivalent is. > > Basically what I am saying is that the metadata for assembling the RAIDs is > on the disks themselves, and the mdadm.conf (if it exists) should be used > for confirmation/security/warning/error reporting purposes ... and not > necessarily for actual assembly. > > > -- > 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 -- 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
