There are several threads related to this issue, but this morning I discovered an even more mystifying side effect of the move to dracut.
First some of the facts that seem to have been illuminated by previous threads.
1 - If you have a /boot on an mdraid volume, even a plain RAID1 mirror, then dracut will ignore it and stall out of the filesystem rebuild operation when booting into recovery mode or running an upgrade from preupgrade or DVD.
2 - If you have two filesystems with the same UUID, the same will happen.
The machine in question is a Fedora 11 i386 box that used to have an mdraid mirrored root file system, and several mdraid mirrored PV components for making up a big volume group for all the rest of the filesystems on the system. Cognisant of the fact 1) above, I split the mirror, zeroed the whole of the second side of the mirror on sdb2 and made sda2 the root filesystem for fstab and grub.conf. I use fdisk to retag the partition as "Linux", then I rebooted and brought the machine back up into full working order. It boots perfectly reliably.
I then ran the preupgrade tool to bring it up to Fedora 13. This again runs through perfectly happily and completes. However, when I attempt to boot into the upgrade grub target, it gets to the part where it is trying to sort out what to mount where and stalls for ages, then gives me a window asking me to select the hard drive on which my root filesystem resides. Selecting anything will bring the same result. Another dialog saying it can't find my root filesystem and a reboot.
Looking on the other tty screens during the long delay, I can see that it is frantically trying to construct a multipath layout that works .. which is inevitably going to fail. I can also see that it seems to expect to see a partition table in the mdraid devices md1 md2 & md3 that make up the physical volume set for the volume group. I wasn't even aware that that was possible now, let alone, apparently mandatory. It used to be utterly illegal.
Please note the following:
- The root/boot filesystem is on sda2
- sda2 is the only partition across the two disks that is tagged "83 Linux" the rest are tagged as "fd Linux raid autodetect"
- sda2 is also flagged as bootable .. just for paranoia.
- sdb2, the former second mirror drive for root, has been zeroed with dd
I do not see how such a basic, simple system could mystify dracut so completely.
Any ideas would be most gratefully received as I have several machines that have either their /boot or the boot/root filesystems under mdraid as this used to be the wise thing to do on small systems. It was taught in Red Hat RHCE courses. I know. I taught it :-)