Before you deploy virtualized solutions, you should understand common architectures as well as the benefits, caveats, pros, and cons of virtualization for servers and services.
Server virtualization versus service virtualization
Operating system virtualization overhead
Disk space used, memory, and CPU
Maintenance (install, configure, upgrade)
Service virtualization has more dependencies
Multiple guests on the same host -- how to do quality of service
Hardware monitoring--on which level
Hardware monitoring with NCS means a service restart (faster)
Hardware monitoring with a virtual machine host means a server restart, with a potentially higher risk of corruption for the virtual machine.
Service monitoring--on which level
Consolidation--on which level
Resource migration--on which level
Server virtualization has more overhead than service virtualization because of emulation of server hardware (main board, NIC, and HBA).
Server virtualization has up to 80% performance loss when compared to native installation on hardware.
When do we realize the performance loss?
Only during high load I/O and not during normal work, such as GroupWise maintenance or database work.
During backup, restore, and data migration.
Whenever we have a high number of small I/O.
Because of the virtualization, higher latency and more CPU usage.
Same patch level for all services is required on one host.
Dependencies exist between services on the same host.
It is impossible to run the same service twice on the same server (isolation).
Processes are not designed to run twice on the same server.
Running multiple instances can cause networking conflicts (ports).
Fewer physical servers and less hardware are required.
Less maintenance for the physical server’s OS is required.
One service can cause a server or other services to crash.
NCS is made to monitor hardware and to monitor services.
VMware is made to monitor hardware and servers. Doing the same thing on multiple layers results in sub-optimal architecture.
Creating multiple cluster nodes on the same virtualization host does not provide the same hardware fault tolerance as having the nodes on separate servers. However, if a guest server fails, you can fail over the resource to another guest server.
Creating multiple clusters within a virtualization environment allows you to maximize the use of your hardware, but it does not provide the same hardware fault tolerance as having clusters running on separate servers.
Performance
CPU and memory
Networks and storage
Fault tolerance
No single point of failure outside the hosts
Resource fail-over matrixes can help assure that you have provided a fail-over environment for each resource
Balancing workload
eDirectory servers
For information about configuring and managing eDirectory servers in your OES environment, see the NetIQ eDirectory 8.8 SP8 documentation website.
The cluster master
Paravirtualization drivers for NIC and SCSI
Manageability
vMotion or virtual machine migration between hosts
Virtual disks versus raw disk mappings
PCI pass-through
20 services need to run on 4 physical servers
Advantages and disadvantages of these solutions
Installation, configuration, and change management
Just NCS hosting 20 resources
Does not have the overhead of a hardware virtualization layer
Has hardware and service dependencies
Just a hypervisor hosting 20 virtual servers
Maintenance overhead
Virtualization overhead
Hypervisor hosting 4 servers with NCS that has 20 resources
Advantages of both the NCS solution and hypervisor solution
The benefits of using both virtualization and NCS include:
Combines server and service virtualization in an intelligent way.
Balances the number of servers with the number of services.
Uses the same rules as NCS on physical environments.
NCS allows you to run fewer virtual servers to provide the same services and allows daytime maintenance.