Diagnosis and Performance Monitoring - Deploying and Managing a Cloud Infrastructure - page 155

as pages, so that it can free up memory space for more urgent applications. This is process
is widely known as paging and that space is called the page file. The size of the page file is
ideally set to 1 percent to 5 percent of the total disk capacity, or it can simply mimic the
size of the memory itself, so if the system has 8 GB of memory, then the swap disk space
should also be 8 GB.
I/O Tuning Moving away from the disks, because their performance is more or less con-
sistent and hardware driven, we set our attentions to I/O operations, which by and large
dictate the work that the disks do and to an extent the CPU wait times that we have to
endure. I/O tuning involves working with the correct number of disks and memory as well
as a lot of scheduling and prioritization. This includes setting buffer times between I/O
calls to the disk. For this process, you must first test the actual performance of the disk
in terms of read and write speeds and then factor that with the actual performance that is
expected of the system, and that will determine the number of disks and the settings that
will be put in place.
Performance Management and Monitoring Tools In any cloud service model, there are
monitoring tools that keep administrators informed about every aspect of the system,
whether it is for IaaS, with monitoring CPU and memory and disk usage levels on the infra-
structure, or for SaaS, with it statistics on user and traffic level as well as application and
virtual environment health. Some solutions cover the entire cloud, from the hardware infra-
structure down to the individual guest OSs running on the system.
Hypervisor Configuration Best Practices The hypervisor is in many ways like an OS,
but it is not as complex and simply serves as an abstraction layer between the underlying
hardware infrastructure and the virtual environment. Since this layer serves to control both
sides of the system, it is essential that all the settings here be just right. For example, the
virtual machines that are running do not know they are virtual and assume that they are
alone and that all computing resources they have are theirs alone, so they tend to go wild
accessing them. It is the job of the hypervisor to, say, limit the number of I/O requests to
the actual disk to prevent overusage by one particular guest OS.
Impact of Configuration Changes to the Virtual Environment As discussed in the previ-
ous chapter, configuration management is important in keeping a system healthy and free
of incompatibilities and security threats. But configuration changes have to be made even-
tually, and understanding the consequences that those changes will be bring is the challeng-
ing part. You also have to keep monitoring any changes being made to the system, in real
time if possible, because unauthorized changes can lead to big problems such as vulnerabili-
ties and even downtime. And in the event of downtime caused by an undocumented and
unforeseen change, the root cause is often hard to track.
Common Issues As a conglomeration of various complicated parts, the computer system
or infrastructure is a well-oiled machine that works well when all the parts are working
and comes to a dead stop when one fails, despite the concept of modularity. In this case,
modularity is geared toward physical assembly and not functionality because most of these
parts are codependent; without one, the whole does not work correctly or at all. That said,
common failure points are the disks (because they feature a lot of moving parts), the NIC,
HBA, memory, and of course, the CPU.