[AFS3-std] More than 13 sites for volume locations

[Harald Barth]

Looks to me that the number of volume copies is limited to 13 by

struct nvldbentry   {
...
        afs_int32       serverNumber[NMAXNSERVERS];     /* Server # for each server that holds volume */
        afs_int32       serverPartition[NMAXNSERVERS];  /* Server Partition number */
        afs_int32       serverFlags[NMAXNSERVERS];      /* Server flags */
...
}

and the same in struct uvldbentry. The question is what to do if I
want to extend this to more. A collegue of mine has a vague memory
that back in the times when IBM did AFS courses some IBM person said
that it was possible to have more than 13 copies anyway, but as I read
the source this must be either some misunderstanding or some other
source ;-) Or do you have more info than I do?

Anyway, if a company is big enough, they want to have a RO copy in
every "site" on the continent or the world or whatever and if they
then have more than 13 "sites", this is the situation they are in.

I have here some speculations how to extend this and I'd be happy if
you would help me with that.

The first idea is to make a bigger array but that is not very
compatible as it is "in the middle" of the struct. It is very mych
wasting space if you have only say 2 servers, too. So I think it would
be better to be able to flag to the cache manager that there are more
servers available so that the client in the next call will ask for
server 14-26 and so on. This has to be flagged somehow, either by
a special last entry or a flag field.

Backwards compat: As allways there is the question of "how backwards
compat is this"? People astonish me allways by using really old
clients. I astonished myself one month ago by booting a Sun4/280
(SunOS4) and the original AFS "just worked". 

My idea here is to keep the first sent struct {n,u}vldbentry "as is"
so that old clients just work as usual with the first 13 volumes. They
don't need to know about copies 14, 15... This can even be enhanced by
presenting the "right" 13 hosts to a client first, for example by
choosing network wise near hosts depending on the cache manager
asking.

Is this a feasible idea?

Is this feature wanted for OpenAFS?

Would such a patch/enhancement be incorporated into OpenAFS?

I see the following steps:

* Make vldb handle more than 13 hosts in the database.
* Make vldb present a choice of 13 hosts to the cm.
* Make cm to ask for more than 13 hosts from the vldb.

How hard do you think this steps will be to implement?

Ehm, if anyone says "it has allready been done" and tells me how, I
would not be unhappy at all.

Harald.