Choosing and Configuring Hardware - Professional SQL Server 2005 Performance Tuning - page 153

64-bitSystemMemoryConfiguration
x 64 and IA64 have a slightly different memory layout from each other and provide each process with a
slightly different amount of VAS. It's roughly 7 TB for IA64 and 8 TB for x 64. Note that Windows Server
2003 SP1 currently only supports a maximum of 2 TB of physical memory.
What this means for SQL Server is that you don't have to worry about using /PAE or /3GB . SQL Server
will have 7 or 8 TB of Virtual Address Space as opposed to 2 or 3 GB in a 32-bit environment.
I/ I/O encompasses both network I/O and disk I/O. In most cases with SQL Server, you are primarily
concerned with disk I/O, as that's where the data lives. However, you also need to understand the effect
that poor network I/O can have on performance.
Configuring I/O for a server storage system is perhaps the place where you have the most options, and
can have the largest impact on the performance of your SQL Server system. When you turn off your
computer, the only thing that exists is the data stored on your hard drive. When you turn the power on,
the processor starts running, the OS is loaded, and SQL Server starts up. All this happens by reading data
and code from the storage subsystem.
This basic concept is true for everything that happens on a computer. Everything starts on the disk, and
has to be read from the disk into memory. From there it moves through the various processor caches
before it reaches the processor and can be used either as code or data. Any results the processor arrives
at have to be written back to disk in order to survive any system shutdown or power cycle (failure,
maintenance, or shutdown).
SQL Server 2005 is very sensitive to disk performance, more so than many applications, because of the
nature of what it does in managing large amounts of data in user databases. Many applications have
the luxury of being able to load all their data from disk into memory and then being able to run for long
periods of time without having to access the disk again. SQL Server strives for that model as it's by far
the fastest way to get anything done. Unfortunately, when the requested operation requires more data
than can fit into memory, SQL Server has to do some shuffling around to keep going as fast as it can, and
it has to start writing data back to disk so it can use that memory for some new results.
NetworkI/O
The network is a key component in any SQL Server system. The network is the link over which SQL
Server receives all its requests to do something and by which it sends all its results back to the client. In
most cases today's high-speed networks provide enough capacity to drive a SQL Server system to use all
its other resources (CPU, memory, and disk) to their maximum potential before the network becomes a
bottleneck.
There are some systems where the type of work being done on the SQL Server is relatively small com-
pared to the number of requests being sent to the server or to the amount of data being returned to the
client. In either of these cases, the network can be a bottleneck.
Network bottlenecks can occur anywhere in the network. This fabric consists of many pieces of net-
work infrastructure, from the simplest system, where two machines are connected over a basic local