Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Thu, Oct 25, 2012 at 12:50:57AM +0200, Rasto Levrinc wrote: > On Wed, Oct 24, 2012 at 11:16 PM, Whit Blauvelt <whit.drbd at transpect.com> wrote: > > I wrote: > > > >> > I've got a fairly simple setup, that back some time ago was working well, > >> > but at some point has slipped away from me. I have a number of KVM VMs which > >> > have been set up by using a distinct LVM partition behind each, and then > >> > using DRBD to mirror these between two servers via a dedicated crossover. > > You mean LVM -> DRBD -> KVM, not LVM->(KVM, DRBD), right? Hmm. Could this be where the administrative error occurs? In terms of installation order it was LVM (on both servers), then KVM (directly to the LVM volume on on server), then DRBD (doing an initial sync from the one server to the other). This may well be where I got stupid, because I accepted the default in LCMC of internal metadata. I have no good reason to think that the raw storage for a KVM VM is compatible with internal metadata. Just wasn't thinking that through. My past use of DRBD has been with file systems (where I've never had a problem with that) not with logical volumes as raw storage. So while I can wish that DRBD (or even LCMC) would be smart enough to complain when asked to used internal metadata in a context where it isn't really sane, there can't be guardrails on everything. For external metadata, the DRBD manual is less than complete. There are a couple of formulas to calculate needed size, but I don't find a step-by-step example. If I were, on installation, to do LVM then DRBD then create the KVM VM on that (as raw storage) would the KVM VM respect the space used by the DRBD metadata? This might actually be an easier process, cloning each of the VMs to a new DRBD-on-LVM pair, than creating external metadata (somehow) for each of the current pairs. But I assume when KVM-QEMU is told to use the LVM as a raw partition, it's just going to use the whole thing, no matter what DRBD's written to the end. Or is it? What's the right way to use DRBD with KVM, when KVM is writing each VM to a dedicated raw LVM volume? If KVM were writing qcows to a filesystem layer, with DRBD behind that filesystem, this becomes a conventional problem. But with the LVM volume being used raw, and a distinct DRBD mirror desired for each KVM VM on raw LVM volume instance, what are the good options? Thanks, Whit