Real World Computing
The promise of petabytes
I'm still recovering from spending a whole afternoon in a far-flung charity branch office, where they'd pressed a donated PC into service as their server while carrying out their good works. Even my traditional emergency machine backup procedure, which involved switching the suffering drive onto the CD IDE cable and building the machine afresh onto a new drive on the primary IDE cable, still left me watching paint dry until well after dark. The "consumer" chipset in their donated PC moved the first few megabytes of files pretty quickly, but getting through 20 gigabytes wasn't what it excelled at.
Even in situations where I would prefer to specify my favourite SCSI controller and a robust, cool-running trio of 36GB drives, every so often I find myself needing to take the low road and, as I've said elsewhere in this column, nowadays Promise is the king of the bottom end in storage matters. That means machines that have the usual twin IDE channels are modified by grafting on a further pair of channels, connected to a PCI expansion slot card. These days, those extra channels might easily be SATA, and lots of people believe it's a good plan to hang two 1TB SATA drives onto a card such as this and then mirror them.
It may not surprise you too much to learn that I disagree heartily with this approach, and for a whole raft of reasons ranging from the simply mechanical (I find 1TB drives to be physically fragile and prone to overheating), to the arcane (a 1TB drive volume has to move a very finely controlled head quite a long way, to home in on your desired data). For my money, a proper RAID array that you're going to store data on has to have three drives, even when money is insanely tight.
But never fear, the basic configuration of a standard PC with twin IDE channels, plus an add-on IDE card with another two, can give you a boot disk plus a three-drive software RAID, defined from within Disk Manager inside Windows. But don't then think there's any further room for scrimping at this level - my favourite cheap-as-chips machine for this role is the Compaq XW6000, which is currently dipping below the £100 mark and is thoroughly under-rated for duties such as hosting a bargain-basement RAID. What makes the difference is that it's a properly built and thought-out dual-processor machine with support for additional PCI card slots that actually expect to be used, and it will run sustained bursts of data flow without tripping over its other peripherals, or due to any cheese-paring on the part of the motherboard's designer.
I know many hardened network admin types will be horrified by the very idea - because no all-IDE solution can hope to serve anything beyond five users simultaneously, no matter how large the connected disks - but there's a neat solution to this. Distributed File Services (DFS) has matured very well in Windows Server 2003 and 2008, and making good use of several machines to present the same set of folders while doing the load-balancing at network level has now become much simpler to implement. And it's perfectly rational to supply the slower sections of that kind of fault-tolerant storage system using simple, trailing-edge bits of technology like the above.
