Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!burl!codas!peora!pesnta!phri!roy From: roy@phri.UUCP Newsgroups: comp.unix.wizards Subject: Re: YP required with NFS? (Really, redundant file servers) Message-ID: <2592@phri.UUCP> Date: Fri, 6-Feb-87 09:25:22 EST Article-I.D.: phri.2592 Posted: Fri Feb 6 09:25:22 1987 Date-Received: Sun, 8-Feb-87 05:29:55 EST References: <2231@brl-adm.ARPA> <59000005@gorgo.UUCP> Reply-To: roy@phri.UUCP (Roy Smith) Distribution: world Organization: Public Health Research Inst. (NY, NY) Lines: 28 In article <59000005@gorgo.UUCP> bsteve@gorgo.UUCP writes: > Lets make them go away and fully abstract the mapping of files across the > network as well as incorporate primary and secondary server hosts for groups > of clients, to make the network more resistant to server crashes. How hard would it be to incorporate a "shadow server" mode into NFS? Imagine 2 servers serving the same file system. When a write request comes in, both servers do it and the client waits to hear an ack from both of them. When a read request comes in, both servers try to do it and the client takes the data from whichever server responds first. When one server goes down, the other one just pick up all the read requests and the write requests only get acked once (there has to be some way for the client to know it's only waiting for a single ack; this is a sticky point). There is nothing new here; schemes like this have been implemented many times before (I think DEC's HSC-50 can do this, for example). Usually, though, it's done at the physical disk level, not the file system level. What kinds of problems would you run into if the two copies of the file system had differing inode numbers, for example? What happens when these two supposedly identical file systems are almost full, but because of slightly different fragmentation, one gets full before the other? What other horrible things might make this idea not work? -- Roy Smith, {allegra,cmcl2,philabs}!phri!roy System Administrator, Public Health Research Institute 455 First Avenue, New York, NY 10016 "you can't spell deoxyribonucleic without unix!"