On 10/12/09 7:55 PM David-Sarah Hopwood <[email protected]> wrote: > ... actually, not even then. I think that servers_of_happiness needs to > be equal to n for the statement on the slide to be correct -- is that > right?
I think so. servers_of_happiness = h guarantees that a successuful upload will place at least one distinct share on each of at least h distinct servers. This means that at least h - k (and possibly more [1]) servers can be lost without any data loss. If n = h, then n - k servers can be lost. Note that this relation only makes sense for h >= k, since h < k would yield negative servers. That case is probably best interpreted (along with h = k) as not assuring any integrity in the event of server failure. [1] The "and possibly more" comes from the rather loose coupling between the peer selection process and the servers_of_happiness behavior. If possible, tahoe-LAFS will attempt to place each of n shares on its own distinct server -- if this succeeds in the case where h is smaller than n, then it is possible to lose more than h servers without losing the file. -- Kevan Carstensen | <[email protected]> _______________________________________________ tahoe-dev mailing list [email protected] http://allmydata.org/cgi-bin/mailman/listinfo/tahoe-dev
