Heinz, I'm having some trouble understanding these answers. Perhaps I am misunderstanding the purpose of a "quorum" on Linux. On AIX, quorums ensure that at least one copy of the latest VGDA is alsays avaialble by ensuring there are always a quorum (over half) of the VGDA copies available. The VGDA is stored on each PV (and sometimes 2 copies are stored on each PV). If you lose quorum, you lose the VG (to ensure we don't varyon with an old copy). You imply that a "quorum" requires ALL of the PVs be avialable in Linux. The dictionary definition of a "quorum", however, is more than half. If a VG in Linux can be varied on with only one good copy of a VGDA (in perhaps a 3-PV VG), then how do you ensure that you are always looking at and updating the most recent copy? If, for instance, I have a 4-disk VG, and I lose 2 disks, then shutdown and varon the VG with the alternate 2 disks (the previously missing ones), I will be seeing only the older VGDA. Is the VGDA also stored in the /etc/lvmtab.d? If so, can you varyon if this VGDA was removed? I guess the big question is: How does LVM for Linux ensure that we are always using the most recent VGDA data (in case we're looking at active PVs that were previously missing). I have to do a lecture to an AIX group on the differences between LVM on AIX and Linux, and quorums were always a big issue for AIX. Thanks, Anthony > > 1) What defines a quorum - over 50% of the PVs in the VG, or over 50% > > of the VGDAs? > > VG quorum is given in case all of its PVs are available. > > > 2) How many VGDAs are stored on each physical volume. From AIX > > experience, this varied depending on the number of PVs in the VG. > > In the LVM1 metadata there's allways 1 VGDA on each PV which has internal > redundancy. > With the new LVM2 formats you can have as many VGDA copies as you like. > > > 3) If quorum is lost on an active VG, is the entire VG automatically > > varied off? > > No, it will stay accessable with the exception of the dead PV(s). > > > 4) Can a VG without quorum be forcefully varied on? > > With LVM1.1 (see CVS; WARNING: his is interim development code!) and with final > LVM2 later this year, you can activate a VG which has lost quorum. _______________________________________________ linux-lvm mailing list linux-lvm@sistina.com http://lists.sistina.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
