On 03/06/2010 06:55 PM, Benjamin Scott wrote: > On Sat, Mar 6, 2010 at 2:15 PM, Jerry Feldman<g...@blu.org> wrote: > >> First I booted into Knoppix 6.2.1, started raid1, pvcreate failed, >> stopped mdadm and did a pvcreate on /dev/sdc2. >> Booted back into Fedora, and I have successfully done a vgextend to >> /dev/md1 ... >> > Ummm... I'm not sure, but I think that will end badly. Both md and > LVM have superblocks (or some other on-disk metadata structure). That > has to use space. So md1 is going to be smaller than sdc2. By > creating the PV on sdc2 (without going through the md layer), LVM is > unaware of the md superblock. I think LVM puts the PV superblock at > the start of the device, and md puts its superblock at the end. So > everything will appear to work until LVM happens to write to the end > of md1, at which point it will (at best) get an "I/O past end of > device" sort of error, or (at worst) overwrite the md superblock. > > The only reason it appears to work at all is that md1 is RAID1 with > one only member, so you can write anything to the non-superblock areas > and the md layer will just pass that back up the storage stack. So > LVM has no way of knowing that the PV superblock it reads from the > start of md1 is not an equivalent device to what it was written to > (sdc2). > > I could be wrong, but that's my take. > > pvck may or may not detect this. > > In any case, I decided to install from scratch. And after allocating the RAID1 volumes and LVMs underneath them, when Fedora (anaconda) went to write to disk it failed. I then redid it cutting the sizes in half so each RAID1 volume was under 500GB. Same error. I then installed SuSE 11.2. It had no problem with the RAID1 and LVM, but at some point it had errors with mounting /dev/md0. I also noted that the partitions were not on cylinder boundaries. I then tried Ubuntu 9.10 but there was no way RAID1 could be set up through the installer. In any case, I then used fdisk to set my partitions on Cylinder boundaries and simply installed Fedora 12 with LVM. The next step is to check bugzilla and and possibly file a problem report, and I'll repeat this exercise after a while. A couple of things I could try without messing up the system is pvcreate with different extent sizes.
-- Jerry Feldman<g...@blu.org> Boston Linux and Unix PGP key id: 537C5846 PGP Key fingerprint: 3D1B 8377 A3C0 A5F2 ECBB CA3B 4607 4319 537C 5846 _______________________________________________ gnhlug-discuss mailing list gnhlug-discuss@mail.gnhlug.org http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
