Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!oliveb!sun!pepper!cmcmanis From: cmcmanis%pepper@Sun.COM (Chuck McManis) Newsgroups: comp.sys.amiga Subject: Re: Diskless nodes (was Re: AM(iga un)IX) Message-ID: <95924@sun.Eng.Sun.COM> Date: 25 Mar 89 18:59:39 GMT References: <72@snll-arpagw.UUCP> <6330@cbmvax.UUCP> <74@snll-arpagw.UUCP> <2421@sbcs.sunysb.edu> <13392@steinmetz.ge.com> <95626@sun.Eng.Sun.COM> <13425@steinmetz.ge.com> Sender: news@sun.Eng.Sun.COM Reply-To: cmcmanis@sun.UUCP (Chuck McManis) Organization: Sun Microsystems, Mountain View Lines: 60 In article <13425@steinmetz.ge.com> (Donald P Perley) writes: >Each of the resources (server-cpu, server-disk, ethernet) are a shared >resource. We probably have close to 500 diskless nodes here, and >dozens of servers. If all of a servers clients are clamouring for >packets at the same time, things can get kind of bogged down. 500 diskless clients and servers on one ethernet is non optimal its true. I would hope you would break those into several IP nets with an occasional server doubling as a gateway (extra ethernet cards are about the same price as a Mac level bridge but _much_ more effective at balancing the network load.) >A resource is easier to share if only one person wants it at a time. Also true. >The thing about your paging file is that your machine is the only one that >needs it, so there is no need to use a shared resource to handle it. >(unless the per megabyte cost is a lot less on the server) This is also true. Lots of people here have been playing with the idea of the "swap" disk. A small, high speed SCSI disk (like the Quantum 40S) that has no file system on it, just swap space. >>The other point you missed (and don't feel bad, most people do) is that >>ethernet is not "split" among the various diskless nodes, it is "given" >>to them. Thus whenever you need it, you get _all_ 1.2 MBytes/Sec of bandwidth >>and don't have to share with anyone. No one makes a disk drive for the >>Amiga yet that can pump out 1.2 Mbytes a second. (Yes they come close, >>but still they aren't there yet.) >Maybe I was mistaken about the nature of ethernet. I thought you only >get it all if no one else is asking. If a server tries to send a packet >can't it get a collision and have to retry? Your mistaken in how ethernet actually works in real life. (Which is different than you would expect it to by reading a description of CD/CSMA type networks) The two key points are that usually the clients and servers are in "sync" which means that the client will use the net to send a packet, and then wait for a reply that the server will send. And that the machine first checks the wire, if there are bits out there it waits until it is clear, otherwise it blasts out a packet. Only if someone else picked that *exact* same time (to within a few dozen microseconds) will there be a collision. The effect in reality is that each participant "sees" a 1.2MByte/s hose that they can use to talk to the other person with. The client sends a request over a 1.2Mb line, and the server answers. Now in the diskless case what actually tends to happen is the the clients will all send a request for a page or what ever and then all go dormant waiting for the server to respond. The server sorts out all the requests and queues them all out to the clients. I agree it is non-intuitive but this is really how it works. --Chuck McManis uucp: {anywhere}!sun!cmcmanis BIX: cmcmanis ARPAnet: cmcmanis@sun.com These opinions are my own and no one elses, but you knew that didn't you. "A most excellent barbarian ... Ghengis Kahn!"