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Dare to be wrong

Posted on 25 Sep 2006 at 12:49

Steve Cassidy is here to tell you that it's okay to ask for help in solving your network nightmares

Quick fixes like adding a multiport Ethernet card such as the Intel PRO/1000 GT (see www.pcpro.co.uk/links/networks145a) were out of the question, as was installing a central switch. Devices that could handle the wide range of connection types he was using can be bought relatively easily, but the process of converting each connection to a pooled setup, then running a single Ethernet interface to either multihome each of the subnets or else route the traffic in a way that emulated the multicard layout was a long-term project best suited to a bank holiday weekend - and that was far too long to wait to do his backup. I know it should have been trivial to re-assign the workstation IP addresses to get out of this multiple-subnet configuration, but he wasn't using DHCP, and touring around the whole site (including the locked executive floor) took more than a complete working day.

This left us with two short-term fixes - run a D2D2T (disk-to-disk-to-tape) backup by beefing up one workstation and moving the tape drives onto it, or try to squeeze more SCSI capability out of the over-filled server. A quick look at all the candidate workstations ruled out the D2D2T option: while money had been spent on the server, the workstations were bargain-basement machines, their cheap tin cases mostly full of hot, sticky dust bunnies and PCI slots on wobbly riser cards. Their onboard Ethernet interfaces were weird, slow and ill-matched to the switches - certainly not up to continuously force-feeding a top-dollar tape drive all night. Upgrading the switches would be just as painful as reconfiguring the server, so back we went and that's when we finally got luck on our side.

The server was a Compaq shed, a double-fronted tower on fat castor wheels with plenty of power and several drive cages. These workhorses are the backbone of the networking business, and despite the fact that they're now turning up on Ebay at £200 a pop for a pallet-load of 12 I still think they have sensible applications if you ignore their CPU rating and focus instead on the number of drives they can fit in, and how well they power, cool and access those drives. The biggest problem with the whole ProLiant range was that seemingly trivial options could make a very large difference to how the whole server operates. I've mentioned here before how often I discover dual- or quad-capable ProLiants toiling away with just a single processor, not enough memory or a paltry pair of 9.1GB SCSI disks, just because the original purchaser had no idea what delights lay waiting in the options section of the catalogue.

My man had gone some way towards collecting the right bits to service his ravenous database application: the server contained separate SCSI RAID cards to service each drive cage, and all three slots available for drives were filled. He'd made rational use of the number of storage devices available in this configuration and distributed his volumes sensibly across the devices. However, when it came to running the tape drives, he'd fallen victim to Options-Catalogue Myopia, compounded by accepting dodgy industry wisdom concerning tape drive misbehaviour. Like all cautious LAN administrators, he'd mounted his tape drives on separate SCSI cards from his RAID arrays, despite each RAID card having an external connector on the back. He'd resisted the temptation to use those and instead drove the tape device via an Adaptec 29160, leaving the two onboard Symbios Logic integrated SCSI, non-RAID chipsets entirely unemployed.

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