Enterprise Library Test Guide - Willy .Net

Testing for Performance and Scalability 217
Performance monitor counter
Avg. Disk Bytes/Read and Avg. Disk Bytes/
Write
Avg. Disk Queue Length
Description and recommendations
Together, these counters represent the size of
the I/O operations. Large I/O sizes can cause
slightly higher disk latency. When you use this
counter to measure SQL Server I/O operations
during the Enterprise Library performance
tests, this value tells you the average size of
the I/O operations that SQL Server issues to
fill query requests.
This counter represents the average number
of read and write requests that are queued for
the selected disk during the sample interval.
The general rule is to ideally have no more
than two requests per spindle. However, this
is difficult to measure because most SANs
use storage virtualization. In reality, this value
may be between 4 requests per spindle and
8 requests per spindle. In general, to detect
problems, look for a higher than average disk
queue length in combination with a higher than
average disk latency. This combination can
indicate that the SAN’s cache is overused.
Monitoring the Network
The primary point of monitoring the network is to check for bottlenecks. To do this,
use the Network Interface\Bytes Total/sec performance counter that belongs to the
Win32_PerfRawData_Tcpip_NetworkInterface class. This counter indicates the rate
at which bytes are sent and received over a network adapter.
Ideally, in a 100 MB network, the approximate value should be13,107,200 bytes/sec.
However, packet control transfers and connection handshakes cause loss, so not all
the bandwidth is available. Usually, this number does not exceed 70 percent of the
total bandwidth. Another often overlooked problem is that the network interface
card (NIC) is set to half duplex instead of full duplex. To find the card’s setting, perform
the following steps.
To determine NIC mode
1. On the taskbar, click Start, and then click Control Panel.
2. Click Network Connections.
3. Right-click the name of your network connection.
4. Click Properties.
5. Click Configure.
6. Click the Advanced tab.