The Need for Speed - Part 5 of 7: A faster computer: performance metrics

So we've covered how to make the most of the particular hardware we might have.  But what if we were to start fresh and try to decide on what hardware would make the most of our software licenses?  I'll try and cover three typical scenarios that seem to come up and how to make the best of them.

I work at a company with Millions and Billions of Dollars in Revenue and purchasing managers who are either very reasonable and accommodating, or maybe even drunk.  What sort of hardware should I purchase for my department?
So there's a few pieces of good news here.

1. Your purchasing managers are in fact very reasonable.  FEA software licenses are very expensive, running into the high 5 figures per year for enough to service a small department.  Compute servers capable of fully exploiting these licenses, on the other hand, are typically in the low 5 figures every few years.   Spending the same amount on software and half as much on hardware could easily halve your analysis throughput for a very small dollar savings.
2. There are fewer options at the high end, which makes decisions about underlying architectures easier.

So on to specifics.  The basic decisions are:

• Hardware Vendor
• Host Operating System
• Processor architecture
• GPUs
• Memory type and quantity
• Hard drive types and RAID type
• Network Interconnects

Hardware Vendor: If you're the sort of company that doesn't build its own multi-acre server farms, just purchase from a company you've heard of before, one that offers long term support contracts.

Host Operating System: Some people will fight the urge to use Red Hat Enterprise Linux 64-bit.  Don't.  Use Red Hat like everyone else.  Spend your time configuring the load monitoring and dispatch software.

Processor Architecture: The most important things are single core floating-point performance, number of cores, and memory throughput.  AMD's Bulldozer architecture and Itanium are out, as both have lost sight of floating point performance as their main performance metric in recent versions.  Nehalem/Westmere are also out, as their memory bandwidth is somewhat lacking at the higher end of CPU count.  This leaves Sandy/Ivy Bridge.  Buy these.  By all means buy the newest and fastest, as many as will fit in one server board.  They'll even come with Intel's Advanced Vector Extensions, which is better supported by Nastran than GPUs.

GPUS: If you use Abaqus, maybe.  If you primarily use Explicit or the unsymmetric solver, then it will be of no benefit.  Otherwise, go ahead.

Memory Type and Quantity: RDIMMS, until no more can be installed.  300GB, 400GB per server.  Special high speed memory modules seem to be losing interest in the market.

Hard drive types and RAID type:  The host operating system doesn't even really needed to be raided for speed.  Long term storage should be offloaded to whatever your organization typically uses.  The speed and capacity of the high speed RAID array will matter more if the output is large, less if it is not.  Order something that seems large enough and that is standard for your vendor.  In contrast to years past, it just won't matter that much.  SSD, 15K RPM server drive, it's not as big a deal as it once was.

Network Interconnects: Consider Infiniband if you do a large amount of Abaqus Explicit or very large/large number of iterations nonlinear Abaqus/Standard models.  Otherwise Gbit Ethernet should suffice. Some Nastran DMP solutions won't see any difference at all, due to how the domains can be seperated.

So spend away!  And laugh in two years at what an outdated piece of junk you can't believe is still around!

I work in a lab at a University and we just received a grant for THOUSANDS OF DOLLARS of server hardware. 

The advice is fairly similar to above.  The most important thing to do is to fill up one server with memory before buying the next, and if you can only partially fill one, stop there.  Whereas tens of GB  is oftentimes sufficient for CFD cluster nodes, hundreds of GB is more desirable for FEA work.  You may very well find yourself with a single server with only half as much memory as the maximum installed, when you could have had half a a dozen boxes on a shelf with less memory.  Don't worry about it, when your models are big there is absolutely no substitute for a big enough chunk of RAM.  And when they're small, several processes on one machine will have much less trouble talking to each other than over a network.

So in short, follow the below list in order until you run out of money:

• Buy a dual socket Sandy Bridge server motherboard, case, power supply, and at least one reasonably large hard drive.  Consider whether you could use a GPU.
• Buy a fast 8-core processor for one of the sockets
• Buy RDIMMS until you've filled half the memory
• Maybe buy a GPU?
• Buy a second 8 core processor
• Buy more RDIMMS until the memory is full
• Maybe buy another GPU? 
• Maybe RAID the hard drive?
• Buy an identical Server and a Gigabit switch.
• Buy Two more servers
• With four servers, start to consider Infiniband, depending on FEA software

That should fairly easily cover the range from a few thousand to 100K or so.

I work for a boss whose bonus is determined by his departments' IT spending.  Our computers are so old we're getting calls from a computer museum in California.

You have two options:

Option 1: Coffee and Crashed Drives
Anything more than two years on any magnetic hard drive is borrowed time.  This time can be significantly reduced if one were to, say, run jobs with far too little memory allotted to them, whilst kicking the case in an attempt to incite a head crash.  When the inevitable happens, tell your boss tales of how if you'd only have enough memory the hard drive wouldn't wear out, plus your computer could run everyone else's jobs and not have to be replaced for a long time.  Your coworkers will now be beholden to you to run their jobs for them, and while they're running you can tell lies about how much it slows down your computer, which is why you're going to get more coffee.

Option 2: Take up a collection (of RAM)
There's a fair chance that some computers in the office are faster than others, and that the computer with the fastest processor has room for more RAM to be installed.  Take as much as can be spared from all the other computers, and load up The Chosen One.  If you're lucky your computer cases will be unlocked and you can actually get at the hardware, and the Chosen One has an X86-64 processor, which has been available since 2007, and have a motherboard that can have more than 4GB of ram installed.  If you're very lucky you'll have a BIOS that will let you boot from a CD-ROM or USB drive, so you can install a free 64-bit Linux operating system alongside Windows XP 32-bit.  If you're very clever you'll then run the old Windows XP inside a virtual machine so a boss passing by will be none the wiser.

And if you get caught, it's always better to ask forgiveness than permission.