EWR@XX.LCS.MIT.EDU.UUCP (04/17/87)
I'd like to pass along this question from one of our system managers. ------- From: RTB "Bob Baynes" 16-APR-1987 14:41 Subj: ETHERNET QUESTION In my experience Ethernet degrades at about 70% its bandwidth (i.e. 7 mbytes). We are thinking of putting a C.Itoh printer on a Decserver 200. My concern is that given the fact that we have three systems (1 VAX 8600, 2 DEC-20s), 150+ users, 4 LN03 printers, and 1 Imagen 8/300 (soon to be connected), placing a C.Itoh printer on the terminal server will push us over the threshold of performance for the network. The assumption is that the C.Itoh printer will print very LARGE files that would have to be transferred between the DEC-20s and the VAX. Can anyone give me any ideas or experience on Ethernet performance with print servers ? -------
oberman@LLL-ICDC.ARPA ("Oberman, Kevin") (04/17/87)
>In my experience Ethernet degrades at about 70% its bandwidth (i.e. 7 mbytes). >We are thinking of putting a C.Itoh printer on a Decserver 200. My concern is >that given the fact that we have three systems (1 VAX 8600, 2 DEC-20s), 150+ >users, 4 LN03 printers, and 1 Imagen 8/300 (soon to be connected), placing a >C.Itoh printer on the terminal server will push us over the threshold of >performance for the network. > >The assumption is that the C.Itoh printer will print very LARGE files that >would have to be transferred between the DEC-20s and the VAX. > >Can anyone give me any ideas or experience on Ethernet performance with print >servers ? First, when an Ethernet degrades is dependent on what response is needed by the components on the net. Under some conditions an Ethernet loaded at less that 70% may be a problem. Second, I don't think you have one. (A problem, that is.) My current Ethernet does quite well with 1-8600, 1-780, 1-785, 4-750s, a dozen uVAXs (running in a Local Area Cluster from one of the 750s), another dozen Sun Workstations with a couple of fileservers and 25 DECservers supporting 150+ users. This net is connected (via LANbridge 100s) to over a dozen other Ethernets with a total of over 400 nodes and thousands of users. There are at least 10 printers on the net although none are extremly heavily loaded. I think it is reasonable to call it a large Ethernet based network. I have a monitor on the net and see a daytime average usage of about 2%. Of course, it's the usage NOW, not the average that counts. And in this area I seldom see the utilization of the net exceed 40% over a .5 second window. This assumes that you are not running any special software to load the net. A MONITOR CLUSTER on one of the nodes will produce noticable spikes of up to 30% usage over the .5 second window. After looking at a number of "heavily loaded" networks I have concluded that few networks are anything like overloaded. And, if one becomes overloaded, the judicious use of LANbridges can easily correct the problem. If you are unsure of the actual load on your Ethernet and can't get a hardware monitor like the LANalyzer or an HP, you might try the MONITOR ETHERNET function as described in previous info-vax messages and in the April '87 Pageswapper page VAX-14. R. Kevin Oberman Lawrence Livermore Nat'l Laboratory arpa: oberman@lll-icdc.arpa (415) 422-6955 Disclaimer: The above is as accurate as I can make it, but with networks, like cars, the milage you get may vary with driving conditions or the phase of the moon. ------