Stephen, In the end the question is one of expectation and view point. The statement in the Admin Guide is that AFS services can be installed on multi-homed machines. It starts off by explaining that "AFS support for multihomed file servers is largely automatic" and why that is the case. It then says "On database server machines, the NetInfo and NetRestrict files determine which interfaces the Ubik database ..."
Of course my reading of this document is colored by the fact that I have read the source code and know the wire protocol and the database formats. As such I know that the only piece of the AFS protocol suite that is multihomed enabled are the UUID enabled VL_GetEntryByNameU and VL_GetAddrsU RPCs on the VL service and the cache manager's management of file server addresses to the file server UUID bindings. DB servers do not have UUIDs but more importantly the UBIK database replication protocol has no support for them or any other mechanism that could associate more than one IP address with a single service. From the perspective of UBIK and all of the DB server clients, each IP address is a distinct server. Since the UBIK master election algorithm relies on the ability to distinguish voting servers and ensure that each (except for the one with the lowest IP address) has only one vote, it is necessary to use NetRestrict, NetInfo and perhaps clones to constrain which interfaces are visible and what they can be used for. Can AFS DB services be deployed on multihomed systems? Yes. Are AFS DB services multihomed capable? No. There are two reasons for using bonded interfaces with a single IP address: 1. Higher maximum throughput 2. Resiliency to network interface or switch failure There is no need to introduce the complexity of multihomed configuration for AFS into the mix. The lack of multihomed support extends beyond the DB servers. The vos commands which in theory could take advantage of knowledge of which addresses are assigned to which file server / volume server do not do so. In AFS 3.4 when the UUID enabled RPCs were added to the VL_ service not all of the required functionality was implemented. In AFS 3.5 the unfinished work was removed. You can call it what you will but as far as I am concerned AFS does not behave on multihomed systems the way one expects that it should. Jeffrey Altman On 9/24/2013 7:04 PM, [email protected] wrote: > I know I've played around with multihomed dbservers before, but it was > long ago, a different use case, on a different platform, and I had > problems then! :-\ > > [edit] I just checked rt.central.org and found my ticket. No update in 9 > years. <https://rt.central.org/rt/Ticket/Display.html?id=15640> > > Anyway, I don't think I'm mis-reading the Admin Guide (but I concede > that what it says may be wrong!) > > In any event, the QuickStartUnix guide also says they can be multihomed: > "It is best to maintain a one-to-one mapping between hostnames and IP > addresses on a multihomed database server machine..." > > But I know all of the openafs docs are often out of date or downright > wrong, which is why I asked on the list. > > As far as you know, is the "it doesn't work" definitive? > > Cheers, > Stephen > > On Tue, 24 Sep 2013, Jeffrey Altman wrote: > >> Stephen, >> >> I believe you are misreading the Admin Guide. It indicates that File >> Servers can be multi-homed and that they self-register. If you have DB >> servers that are multi-homed you need to pick a single network interface >> for them to use >> >> If given the choice of interface bonding and multi-homed, choose bonding. >> >> Jeffrey Altman >> >> On 9/24/2013 6:01 PM, [email protected] wrote: >>> I have two general questions about multihomed AFS servers to pose to >>> list. >>> >>> >>> - Is there any obvious reason to choose multihoming of a fileserver >>> rather than link aggregation, assuming both are supported in a given >>> environment? >>> >>> >>> - The Admin Guide on docs.openafs.org indicates that multihomed DB >>> servers work.[1] >>> >>> Is this true in an environment where both IPs are on the same (campus) >>> network and they may share the same default route? >>> >>> Specifically, I'm curious about linux dbservers; clients may contact the >>> server via IP A but get an answer from IP B, if it is the default >>> interface. Will the clients care? What if the IP replying isn't in the >>> client's CellServDB (or DNS) at all? Does the answer change depending on >>> client version? >>> >>> [1] <http://docs.openafs.org/AdminGuide/index.html#HDRWQ138.html> >>> >>> Cheers, >>> Stephen >>> >>> _______________________________________________ >>> OpenAFS-info mailing list >>> [email protected] >>> https://lists.openafs.org/mailman/listinfo/openafs-info >> >> > _______________________________________________ > OpenAFS-info mailing list > [email protected] > https://lists.openafs.org/mailman/listinfo/openafs-info
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