On Dec 15, 11:51, Sellam Ismail wrote: Indeed. I can tell you a story about that... A few years ago, our Department tendered for a Novell server, to act as file and mail server for our student network. The tender was won by A Well-Known PC Company with 4 letters in their name (how appropriate, as it turned out) who supplied the hardware and on-site maintenance. Well, the on-site maintenance came in the form of trained monkeys who were moderately capabable of, say, swapping a disk drive, and not very good at solving problems when the system went wrong -- as it did, rather frequently. So frequently, in fact, that for a while the Department insisted a rota for support staff "on call", something which as far as I know, has never been done before. After many "discussions" with the trained monkeys and their management, who insisted that our experienced and qualified staff must not taper with "their" hardware, we stopped calling them, and did some tests. Basically, the power supply couldn't cope with the sum of the disks and RAM. To solve the problem properly (after adding a second PSU and moving all the disks to separate housings) it was decided that we'd buy a replacement system, from another Computer Company of high repute (this one with six letters in its name). The new, overkill, spec was for dual-processor, two banks of ECC RAM, triple redundant hot-swappable power supplies, hot-swappable RAID disks, two network interfaces, and a UPS. And just for good measure, we wanted a pair of these, linked directly by a crossover cable on the second network interfaces, and running some smart software that allowed one to mirror the other. In theory, if the "live" server failed, the other would adopt its IP address and take over. In theory, theory and practice are the same. In practice, they are different. In practice, our network turns out not to like duplicate IP addresses, that is, two devices with different MAC addresses but using the same IP address -- and the second machine was not always perfectly silent. In practice, the backup server was always a bit too enthusiastic. The live server would see a glitch on the RAID disks and report it, and the backup would try to take over. But the live one wouldn't let go, and they'd fight. Almost daily, partly because the RAID system was perfectly capable of correcting errors much of time, but its controller was perfectly capable of generating them as well. In the end, we found it better to switch one off. The live one fails only occasionally, usually when doing an overnight backup. And we have a heavy box to prop open the machine room door. Or run VMware from time to time. Moral: there is such a thing as overkill, and such a thing as over-engineering. -- Pete Peter Turnbull Network Manager Dept. of Computer Science University of York