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. -- Ben _______________________________________________ gnhlug-discuss mailing list gnhlug-discuss@mail.gnhlug.org http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
