Date: Wed, 20 Jun 2007 17:36:23 -0400 (EDT) From: "Stuart D. Gathman" <stuart@bmsi.com> On Wed, 20 Jun 2007, Richard van den Berg wrote: > To answer my own question: when a pv is not available at boot time, the > vg using that pv does not come up. So splitting vgs makes sense when you > want to minimize the impact of one disk failure. Hmmm. On AIX LVM, vgs still boot when physical volumes fail, provided there is a "quorum". The metadata is redundantly stored on all PVs, so a "quorum" means that more than half of the metadata copies are available and at the same version. I think Linux LVM stores only metadata for that PV on a PV, but there is a backup in /etc/lvm. If the system truly won't boot with a failed disk, that kind of adds another reason why current LVM mirroring support is useless. I can also confirm that Linux LVM won't activate a VG that's missing PVs. Under Ubuntu Breezy, I had a VG divided into one tiny LV for the usual OS dirs (/bin /etc /home /var etc etc) and one large LV (spanning both the boot disk and a second disk) for a single large filesystem. While I was doing some hardware reconfiguration (details irrelevant), I tried booting with the second disk disconnected, and LVM couldn't activate any of the VG, including the LV that held the OS itself, even though that LV definitely didn't cross into the second disk. (It was created months before the second disk was added, was never extended, and thus consisted of a single PV.) Once I discovered that, and since I was reconfiguring how its disks worked anyway, I started over and created two VGs. The first held a single LV, which held the OS, and the second VG held another LV, which spans boths disks and holds the large filesystem. -That- will boot with the second disk disconnected: the first VG is activated and the OS boots, and the second VG won't activate (unless, I assume, I force it with --partial) because it's missing one of its PVs, but since the filesystem that the OS is on isn't in that VG, at least the machine boots. (Yes, it'd probably be possible to make my own initrd that did everything the normal one does but supplies --partial in the right place, but that'd be a total pain to keep up-to-date across every automatic kernel update, etc. Given that I knew I'd be blowing away the entire disk structure and starting over, it was far easier to just create two VGs; presumably there'd have been some sneaky way [not using the normal LVM API] to have changed the on-disk data structures in-place if I'd been desperate, since in theory nothing about the size or placement of the LVs would necessarily have changed.) _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/