SMP Provides A Mirror Into Your Server
How Tolerant Is Your Server?
Server vendors like to play on your fears when selling you fault tolerance and, in the process, jack up the sticker price. But don't be too skeptical about fault tolerance. As my dad used to say, "Just because you're paranoid doesn't mean they aren't really out to get you." Features that have been standard on Unix superservers for years are starting to appear in the Intel-based machines. Fault-tolerant features make your server more than just a desktop machine on steroids.
Look for hot-pluggable components. Sure, we've had hot-pluggable hard drives for years now, but some servers, like Dell Computer Corp.'s PowerEdge 4100 and 6100, even have hot-pluggable SCSI
backplanes.
Do you want hot-pluggable, redundant power supplies? I have always been suspicious of redundant power. After all, if you have two power units in your server and you lose power to the building, what's the difference? Still, something could actually go wrong with the power supply itself--like that time you kicked the power cord out of the wall socket when you were moving something behind the server.
How about redundant or hot-pluggable fans? These I like. I've seen a $1,000 disk drive die when a $1.95 muffin fan stopped spinning. It wasn't pretty. Just about any server you choose will have management software that alerts you if a fan stops. The better ones will warn you if a fan is about to stop, so you can replace the fan without bringing down the server.
Redundant NICs eliminate another potential point of failure. Compaq's Network Control Utility lets you configure two network cards as a merged pair. The network sees them as a single card. If one fails for any reason, the second car
d takes over without losing connectivity.
One key feature that separates the server from the desktop is server management software. Products like Compaq Insight Manager and Hewlett-Packard Co.'s HP NetServer Assistant let server administrators watch th
e server remotely. They receive notification not only of failures, but also of potential failures of fans, disk drives, memory, power and network cards. These notifications can come as pages, e-mail or Simple Network Management Protocol (SNMP) traps sent to a network management console like HP OpenView.
Many server manufacturers offer prefailure warranties on their servers. For example, if the server tells you its disk drive is about to fail, just call the manufacturer and a new disk drive will be in the mail. You can replace a failing hot-pluggable drive and have the array rebuilt without users ever being aware of a problem.
How Free Is Free Tech Support?
I'm not going to preach to you about technical support. Just keep in mind that it's
no use getting those prefailure alerts from your server if you can't get the replacement component delivered before the old one fails. Be prepared to pay for premium support--then be sure you get it.
Now that you know what to look for in a server, let's discuss SMP specifically. An SMP server has multiple CPUs, each sharing identical tasks and each having access to the same memory, drives and I/O bus. All are running the same instance of the network operating system. SMP then divides the work among these groups, connecting them through a high-speed bus. SMP is not the same as high-end massively parallel processing (MPP) machines with hundreds of CPUs running multiple copies of the NOS. Nor is it the same as Non-Uniform Multiprocessing Architecture (NUMA), which basically provides clustering in a can.
There are three main components to consider when putting together an SMP server: memory, storage and CPUs. First, you must decide if you need multiple processors. Achieving significant performance impr
ovements by simply tuning your application is possible, while adding processors to a server may not get you the performance you expect.
In "Making Your Server System Scale" (see March 15, page 140), senior technology editor Jay Milne found that when he added CP
Us to his test server, there was no corresponding increase in transactions per second. But after making one simple modification to the SQL database running on the server, transactions per second increased by 15 percent. If you find you need more horsepower even after tweaking your application, consider adding memory or redesigning your drive array before adding processors.
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