Measurement
Technologies
There are several different measurement technologies that can be used to provide data. To be successful, a technology needs to be widely accepted, efficient, useful, and very general. The following discusses some different technology and hopefully you will come to the conclusion that there are many 'less than perfect' approaches.
Measurement Options
Control Blocks analysis is
standard technology when there is nothing better. The problem
with using control blocks is that if the control blocks change,
so does the measurement facility.
In VM, many performance monitors make extensive use of the
CP Diagnose command to acquire data. The monitors are often
months if not years behind in support of new releases of VM.
And supporting new releases of VM may be cost prohibitive,
leaving the users without monitors when the system is upgraded.
In UNIX, the analogy is dev/kmem, giving program access to kernel
data. With over 100 unix variants, maybe thousands of monitor
variants were required to retrieve data. Thus no dev/kmem based
monitor exists that claims to monitor all flavors of Unix.
For IP stacks, the analogy continues to netstat.
The netstat command is an interface to TCPIP control blocks.
These control blocks certainly contains useful information, but
each tcpip stack and each level of that stack requires a netstat
that can read the control blocks.
Standard Interface exist that do not have the same drawbacks.
For VM, there is the CP Monitor. When VM changes, the monitor
is upgraded concurrently. The standard interface provided by
the CP monitor means that one version or release of a
monitor product (such as ESAMAP or ESAMON)
can support any release of VM/XA, VM/ESA or z/VM. Old releases
of ESAMON still operate on z/VM. And ESAMON and ESAMAP were
updated in just a few hours to fully support z/VM.
For network data, there is the same type of standard interface -
SNMP, Simple Network Management Protocol. Using standard SNMP
data requests, data from almost any network device or host is
available in a standard format. ESATCP uses this protocol
to collect data to report network traffic and errors. When
TCPIP is updated or enhanced, ESATCP keeps operating without change. APPLMON)
If you were to provide an ideal monitor for linux, what would the architecture be? Hopefully something as easy to use as SNMP or the VM Monitor facility.
Examples of using Technology
PING
Ping is widely used as a measurement facility, because it
can measure a specific
connection at a specific time.
But PING does not measure user traffic, only a given response time
between two nodes at a given time. Thus, unless you have a tool
that evaluates all your current connections and performs pings
at approximately the same time as the users are transmitting data
the data will vary widely from end user perception. There are several
other objections to using ping, the best heard yet was that an
installation turned off the ping based monitor and network traffic
dropped 40%. A monitor should not cause performance problems...
Browser Applets
Another technology sends out a java applet to run in the browser
to measure the user's transactions from the user's perspective.
If your users allow java to run on their browsers, this can
provide data for a web application, but web is not the only
IP application. A more general approach is required to ensure
consistent data is available for all applications.
NETSTAT
Almost all IP stacks provide a netstat command to provide performance
data of the network applications. The issue
with netstat is how would you collect this data for hundreds
of servers? Logon to each server and acquire the data manually?
or write an interface that then sends the data back to a central
server for analysis? Certainly doable, but when you have
different levels of software on all your servers, who is going
to update all the interfaces? is this an issue?
SNMP
The standard SNMP data is referred to as MIBII. This is what provides
instrumentation on network traffic and errors.
There is also a set of HOST MIBS defined that measures the
host resources. This implementation is discussed in
SNMP.
RMFPMS
RMFPM is an agent provided by IBM from the zSeries Performance
Management Development organization. This
Free agent runs under
linux. This implementation
is discussed in RMFPMS.