Key Windows Performance Counters, Info and Limits

June 21, 2012 microsoft, Performance No comments

Key Windows Performance Counters, Info and Limits

Counter

Description

What to watch for
Logical Disk\% Free Space Measures the percentage of free space of the selected Logical Disk If it is below 15% then you run the risk of running out of space to store critical O/S files
PhysicalDisk\Idle Time Measures the percentage of time the disk was idle during the sample interval If this value falls below 20% the disk system is said to be saturated and you should install a faster disk system
PhysicalDisk\Avg. Disk Sec/Read Measures the average time in seconds to read data from the disk If this value is larger than 25 milliseconds the disk system is experiencing latencyFor SQL and Exchange the threshold is lower – 10ms
PhysicalDisk\Avg. Disk Sec/Write Measures the average time in seconds to write data from the disk If this value is larger than 25 milliseconds the disk system is experiencing latencyFor SQL and Exchange the threshold is lower – 10ms
Physical Disk\Avg Queue Length How many I/O Operations are waiting for the Hard Drive to become available If the value of the counter is larger than twice the number of disk spindles in an array then the disk may be a bottleneck
Memory\Cache Bytes Indicates the amount of memory being used for the file system cache. There will be a bottleneck if the value is greater than 300MB
Processor\%Idle Time % Idle Time is the percentage of time the processor is idle during the sample interval Below 20% and you are running at CPU saturation if this prolonged
Processor\Interrupts/sec The numbers of interrupts the processor was asked to respond to. Interrupts are generated from hardware components like hard disk controller adapters and network interface cards. A sustained value over 1000 is usually an indication of a problem. Problems would include a poorly configured drivers, errors in drivers, excessive utilization of a device (like a NIC on an IIS server), or hardware failure
Processor\%Processor Time Measures  how much time the processor actually spends working on productive threads and how often it was busy servicing requests. It actually provides a measurement of how often the system is doing nothing subtracted from 100%. This is a simpler calculation for the processor to make. The processor can never be sitting idle waiting to the next task, unlike our cashier. The CPU must always have something to do. It’s like when you turn on the computer, the CPU is a piece of wire that electric current is always running through, thus it must always be doing something. NT give the CPU something to do when there is nothing else waiting in the queue. This is called the idle thread. The system can easily measure how often the idle thread is running as opposed to having to tally the run time of each of the other process threads. Then , the counter simply subtracts the percentage from 100%. This counter is a natural choice that will give use the amount of time that this particular process spends using the processor resource.
Memory\Page Faults/sec This counter gives a general idea of how many times information being requested is not where the application (and VMM) expects it to be. The information must either be retrieved from another location in memory or from the pagefile. While a sustained value may indicate trouble here, you should be more concerned with hard page faults that represent actual reads or writes to the disk. Remember that the disk access is much slower than RAM
Memory\%Committed Bytes in use This counter indicates the total amount of memory that has been committed for the exclusive use of any of the services or processes on Windows NT. Should this value approach the committed limit, you will be facing a memory shortage of unknown cause, but of certain severe consequence.
Memory\Available Bytes This counter indicates the amount of memory that is left after nonpaged pool allocations, paged pool allocations, process’ working sets, and the file system cache have all taken their piece.
System\System Calls/sec This counter is a measure of the number of calls made to the system components, Kernel mode services. This is a measure of how busy the system is taking care of applications and services—software stuff. When compared to the Interrupts/Sec it will give you an indication of whether processor issues are hardware or software related. See Processor : Interrupts/Sec for more information
System\Threads Threads is the number of threads in the computer at the time of data collection. This is an instantaneous count, not an average over the time interval.  A thread is the basic executable entity that can execute instructions in a processor. Monitor loosely
System\Processor Queue Length Gives an indication of how many threads are waiting for execution. If this counter is consistently higher than around 5 when processor utilization approaches 100%, then this is a good indication that there is more work (active threads) available (ready for execution) than the machine’s processors are able to handle. Note that this is not always a hard and fast indicator however, for some services like IIS 6 pool and manage their own worker threads, so on a busy web server for example you would want to look at other counters like ASP\Requests Queued or ASP.NET\Requests Queued as well. Furthermore, the larger the number of active services and applications running on your server, the busier the processor queue will normally be, so on a multi-role server running near 100% utilization content may only be a significant factor once System\Processor Queue Length exceeds something like 10 instead of 5 as mentioned previously.
Network Interface : Bytes Sent/sec This is how many bytes of data are sent to the NIC. This is a raw measure of throughput for the network interface. We are really measuring the information sent to the interface which is the lowest point we can measure. If you have multiple NIC, you will see multiple instances of this particular counter. Dependent on NIC Speed
Network Interface: Bytes Received/sec. This, of course, is how many bytes you get from the NIC. This is a measure of the inbound traffic In measuring the bytes, NT isn’t too particular at this level. So, no matter what the byte is, it is counted. This will include the framing bytes as opposed to just the data Dependent on NIC Speed

 

Storage/Datastore Reclamation in VMware

June 21, 2012 Storage, VMware No comments

Sometimes, it is worth doing a storage reclamation exercise through all your VMware Datastores in order to remove old folder, files and to check that nothing miscellaneous is going on.

What can you find?

In vCenter > Datastores > Performance Tab, you can find the graph showing all the files it can detect with the selection “Other VM Files” OR “Other” which is what we’re interested in.

When we checked this out on the Host back-end logged in via Putty, we can see the below. The ./ files are not usual to find on LUNs/Datstores and indicate that there are SAN snapshots existing on here

/vmfs/volumes/4e0da454-902c23bf-cb36-e61f13f7c69b # ls -l

SERVER01
SERVER02
SERVER03

/vmfs/volumes/4e0da454-902c23bf-cb36-e61f13f7c69b # find . -exec ls -lh {} \; | grep flat

SERVER01-flat.vmdk
SERVER01_1-flat.vmdk
SERVER01_2-flat.vmdk
SERVER01_3-flat.vmdk

./SERVER01/SERVER01_3-flat.vmdk
./SERVER01/SERVER01_2-flat.vmdk
./SERVER01/SERVER01_1-flat.vmdk
./SERVER01/SERVER01-flat.vmdk

Conclusion

You will need to ask your Storage Admin to check out your LUNs and make sure that any old snapshots are either required or can be deleted.

It is worth keeping an eye on all of this as we found we had nearly 2TB of LUN Snapshots lurking around taking up valuable and expensive storage space.

Reliability Monitor in Windows 2008

June 19, 2012 microsoft, Performance No comments

Reliability Monitor is an advanced tool which measures hardware and software problems and changes to the computer. It provides a stability index which ranges from 1 (Least Stable) to 10 (Most Stable)

Accessing Reliability Monitor

You can access it 2 ways.Either by typing in perfmon/rel or following the steps below

  • Open Action Center
  • Click Maintenance
  • Then under Check for Solutions to Problem Reports, click View Reliability History

What can you do?

  • Click on any event on the graph to view details
  • Click Days or Weeks to view the stability index
  • Click items in the Action Pane to view more info about it
  • Click View All Problem Reports to view only the problems that have occurred on your computer

Gathering System Stability Data

The Reliability Monitor displays data gathered by the Reliability Analysis Component (RAC) This is implemented using RACAgent.exe which is scheduled to run once an hour. Reliability Monitor starts displaying a system stability index rating and specific event information 24 hours after system installation, and the RACAgent task runs by default after that O/S is installed. If it has been disabled, it must be manually enabled from the Task Scheduler snap-in for the MMC.

Enable RACAgent

To enable to RACAgent Task, you must use an account which is a member of the Local Administrators Group on the computer.

  • Click Start > Search > Type taskschd.msc
  • Expand Task Scheduler Library
  • Expand Microsoft
  • Expand Windows
  • Select RAC
  • Right click RAC and select View and Show Hidden Tasks
  • In the Results Pane, right click RACAgent and select Enable

Performance and Resource Monitoring in Windows Server 2008

June 19, 2012 microsoft, Performance No comments

What does Windows Reliability and Performance Monitor do?

Windows Reliability and Performance Monitor is a Microsoft Management Console (MMC) snap-in that combines the functionality of previous stand-alone tools including Performance Logs and Alerts, Server Performance Advisor, and System Monitor. It provides a graphical interface for customizing performance data collection and Event Trace Sessions.

It also includes Reliability Monitor, an MMC snap-in that tracks changes to the system and compares them to changes in system stability, providing a graphical view of their relationship

What new functionality does this feature provide?

Features of Windows Reliability and Performance Monitor new to Windows Server 2008 include the following.

Data Collector Sets

An important new feature in Windows Reliability and Performance Monitor is the Data Collector Set, which groups data collectors into reusable elements for use with different performance monitoring scenarios. Once a group of data collectors are stored as a Data Collector Set, operations such as scheduling can be applied to the entire set through a single property change.

Windows Reliability and Performance Monitor also includes default Data Collector Set templates to help system administrators begin collecting performance data specific to a Server Role or monitoring scenario immediately.

Wizards and templates for creating logs

Adding counters to log files and scheduling their start, stop, and duration can now be performed through a Wizard interface. In addition, saving this configuration as a template allows system administrators to collect the same log on subsequent computers without repeating the data collector selection and scheduling processes. Performance Logs and Alerts features have been incorporated into the Windows Reliability and Performance Monitor for use with any Data Collector Set.

Resource View

The home page of Windows Reliability and Performance Monitor is the new Resource View screen, which provides a real-time graphical overview of CPU, disk, network, and memory usage. By expanding each of these monitored elements, system administrators can identify which processes are using which resources. In previous versions of Windows, this real-time process-specific data was only available in limited form in Task Manager.

Reliability Monitor

Reliability Monitor calculates a System Stability Index that reflects whether unexpected problems reduced the reliability of the system. A graph of the Stability Index over time quickly identifies dates when problems began to occur. The accompanying System Stability Report provides details to help troubleshoot the root cause of reduced reliability. By viewing changes to the system (installation or removal of applications, updates to the operating system, or addition or modification of drivers) side by side with failures (application failures, operating system crashes, or hardware failures), a strategy for addressing the issues can be developed quickly.

Unified property configuration for all data collection, including scheduling

Whether creating a Data Collector Set for one time use or to log activity on an ongoing basis, the interface for creation, scheduling, and modification is the same. If a Data Collector Set proves to be useful for future performance monitoring, it does not need to be re-created. It can be reconfigured or copied as a template.

User-friendly diagnosis reports

Users of Server Performance Advisor in Windows Server 2003 can now find the same kinds of diagnosis reports in Windows Reliability and Performance Monitor in Windows Server 2008. Report generation time is improved and reports can be created from data collected by using any Data Collector Set. This allows system administrators to repeat reports and assess how changes have affected performance or the report’s recommendations.

Accessing Performance Monitor

Membership in the local Performance Log Users group, or equivalent, is the minimum required to complete this procedure.

To start Performance Monitor

  • Click Start, click in the Start Search box, type perfmon, and press ENTER.
  • In the navigation tree, expand Monitoring Tools, and then click Performance Monitor.

You can also use Performance Monitor to view real-time performance data on a remote computer.

Membership in the target computer’s Performance Log Users group, or equivalent, is the minimum required to complete this procedure

To view performance counters from a remote computer, the Performance Logs and Alerts firewall exception must be enabled on the remote computer. In addition, members of the Performance Log Users group must also be members of the Event Log Readers group on the remote computer

Creating Data Collection Sets

A Data Collector Set is the building block of performance monitoring and reporting in Windows Performance Monitor. It organizes multiple data collection points into a single component that can be used to review or log performance. A Data Collector Set can be created and then recorded individually, grouped with other Data Collector Set and incorporated into logs, viewed in Performance Monitor, configured to generate alerts when thresholds are reached, or used by other non-Microsoft applications. It can be associated with rules of scheduling for data collection at specific times. Windows Management Interface (WMI) tasks can be configured to run upon the completion of Data Collector Set collection.

Data Collector Sets can contain the following types of data collectors:

  • Performance counters
  • Event trace data
  • System configuration information (registry key values)

Real Time Example

  • Start Performance Monitor
  • Right-click anywhere in the Performance Monitor display pane, point to New, and click Data Collector Set. The Create New Data Collector Set Wizard starts. The Data Collector Set created will contain all of the data collectors selected in the current Performance Monitor view.

  • Type in a name for your Data Collection Set and Choose from Template

  • Choose a Template (System Performance for this example)

  • Choose where the Data is going to be saved

  • Choose who to run this as. If you have permissions then this can be left as default. Choose to open the properties for this job

  • The General Tab

  • Click Directory

  • Click Security

  • Click Schedule

  • Stop Condition

  • Click Task

Reports

When this job has finished, Performance Monitor will reconcile a report to show the full history of this job.

Analysing the Results

Data Analysis
A tool that Microsoft support relies on to analyze Performance Monitor logs is the Performance Analysis of Logs (PAL) Tool. Clint Huffman, a Microsoft senior premier field engineer, wrote the 6,000-line VBScript tool, which is free and open source. PAL lets administrators easily analyze Performance Monitor logs without requiring them to be experts in performance counters or Windows architecture.

PAL contains a wizard-based UI that asks specific information about the system, which PAL passes as arguments to the VBScript program. PAL picks up where other log analyzers leave off, such as taking into account whether the system is 64-bit or 32-bit, whether the /3GB switch is used, and how much physical memory is installed—all variables that affect system performance. PAL uses these variables along with known thresholds, which were determined by engineers with years of experience, to determine the analysis that’s displayed. PAL provides a chronological order of alerts, so that you can correlate your system’s performance to any problems that you noticed at specific times.

Counters and Limits

http://technet.microsoft.com/en-us/library/cc768048.aspx

Planning a Terminal Services Deployment

June 16, 2012 microsoft, Terminal Services No comments

The first step in planning a deployment is understanding how the following Terminal Sever components fit together

  • Terminal Server

The server itself is at the core component of a Terminal Services deployment. This is the server that the clients connect to so they can access their applications

  • Terminal Server Farm

A Terminal Server farm is a collection of Terminal Servers used to provide high availability and load balancing to clients on an organisational network. Client connections to Terminal Server Farms are mediated by Terminal Services Session Directory Servers. Terminal Server farms are more likely to be deployed at large sites than small ones

  • License Servers

License servers provide Terminal Server Client Access Licenses (TS CALS) to Terminal Servers on the network. Unless a license server is deployed, clients are only able to connect to Terminal Services for a limited time only.

  • Terminal Services Gateway Servers (TS Gateway)

These servers provide access to Terminal Servers to clients on untrusted networks. In Enterprise networks, you can use a TS Gateway server as a bridge between the standard internal network and a Terminal Server farm on a network protected by server isolation policies

Terminal Server Licensing

All clients that connect to a Terminal Server require a TS CAL. This license is not included with the O/S a client uses or a standard server license.

TS CALs are managed by a Terminal Server Licensing server

  • What is the scope of the licensing server. Will it service clients in the domain or workgroup or manage the licenses for all clients in the forest
  • How will the license server be activated with Microsoft. Automatic, Web Browser or Telephone
  • How many license servers do you need for your organisation?
  • What type of licenses will be deployed

Terminal Server Session Broker

The Terminal Server Session Broker service simplifies the process of adding more capacity to an existing Terminal Services Deployment. It enables Load Balancing of terminal services in a group and ensures the reconnection of clients to existing sessions in that group. In Terminal Server Session Broker, a group of Terminal Servers is called a Farm.

The Terminal Server Session Broker is a database which keeps track of TS sessions. TS can work with DNS Round Robin or with NLB. When configured with NLB, the Terminal Server Session Broker Service monitors all servers in the group and allocates clients to to the servers which have the most amount of free resource.

When used with DNS Round Robin, clients are still distributed, the main benefit being is that Terminal Server Session Broker remembers where a client is connected. TS Load Balancing is restricted to Windows 2008 Terminal Servers only

Clients must support RDP 5.2 or later

Each Terminal Server must have the same application configuration

The following diagram provides a more detailed representation of the traffic flow. In the diagrammed scenario, all terminal servers in the farm have host resource records in DNS that map to the terminal server farm name (“Farm1”). Therefore, any terminal server in the farm can act as a redirector and process the initial connection requests

http://technet.microsoft.com/en-us/library/cc772418(v=ws.10).aspx

Terminal Server Gateway Server

Plan the deployment of Terminal Server Gateway Servers when you need to enable RDP over HTTPS connections to RDP Servers located on Protected internal networks to clients on the internet or untrusted networks. TS Gateway servers are not limited to screened subnets between internal networks and the internet but can also be deployed to enable access to servers that are the subject of IPsec isolation policies

Network Connectivity Status Indicator and Resulting Internet Communication in Windows 7 and Windows Server 2008 R2

June 14, 2012 microsoft, Networking No comments

NCIS

Windows® 7 and Windows Server® 2008 R2 include a feature called Network Connectivity Status Indicator (NCSI), which is part of a broader feature called Network Awareness. Network Awareness collects network connectivity information and makes it available through an application programming interface (API) to services and applications on a computer running Windows 7 or Windows Server 2008 R2. With this information, services and applications can filter networks (based on attributes and signatures) and choose the networks that are best suited to their tasks. Network Awareness notifies services and applications about changes in the network environment, thus enabling applications to dynamically update network connections.

Network Awareness collects network connectivity information such as the Domain Name System (DNS) suffix of the computer and the forest name and gateway address of networks that the computer connects to. When called on by Network Awareness, NCSI can add information about the following capabilities for a given network:

  • Connectivity to an intranet
  • Connectivity to the Internet (possibly including the ability to send a DNS query and obtain the correct resolution of a DNS name)

What you will see

A yellow warning triangle in the System Tray looking like

and

What does Windows check, and in what order, before it announces that there are connectivity problems and displays the yellow triangle formed icon down at the task bar

Windows checks a Microsoft site for connectivity, using the Network Connectivity Status Indicator site.

  • NCSI sends a DNS lookup request for dns.msftncsi.com. This DNS address should resolve to 131.107.255.255. If the address does not match, then it is assumed that the internet connection is not functioning correctly.

The exact sequence of when which test is run is not documented; however, a little bit of digging around with a packet sniffing tool like Wireshark reveals some info.

It appears that on any connection, the first thing NCSI does is requests the text file (step 1 above). NCSI expects a 200 OK response header with the proper text returned. If the response is never received, or if there is a redirect, then a DNS request for dns.msftncsi.com is made. If DNS resolves properly but the page is inaccessible, then it is assumed that there is a working internet connection, but an in-browser authentication page is blocking access to the file. This results in the pop-up balloon above. If DNS resolution fails or returns the wrong address, then it is assumed that the internet connection is completely unsuccessful, and the “no internet access” error is shown.

The order of events appears to be slightly different depending on whether the wireless network is saved, has been connected to before even if it is not in the saved connections list, and possibly depending on the encryption type. The DNS and HTTP requests and responses showing up in Wireshark were not always consistent, even connecting to the same network, so it’s not entirely clear what causes different methods of detection under different scenario

Resolving this issue

  • http://technet.microsoft.com/en-us/library/ee126135%28v=ws.10%29.aspx
  • Check you can ping your DNS Servers
  • Check you can ping your Gateway
  • Check your server is listed correctly in DNS
  • Check DNS suffixes
  • Check proxy servers if you have any
  • Check your router
  • Check other servers have connection
  • Turn off the Indicator in Group Policy.
  • If everything checks out ok, Go into GPMC and Expand Computer Configuration, expand Administrative Templates, expand System, expand Internet Communication Management, and then click Internet Communication settings. In the details pane, double-click Turn off Windows Network Connectivity Status Indicator active tests, and then click Enabled
  • Change the Registry key to not query the server:  HKLM/system/currentcontrol
    set/services/nlasvc/parameters/internet – set enable activeprobing to 0

Remote Desktop Login always creates a temporary profile

June 13, 2012 microsoft, Terminal Services No comments

Just a quick fix for this as this happened to me today and is a fairly annoying problem

Resolution

  • Log into server as an Administrative User
  • Start > Run regedit
  • [HKEY_LOCAL_MACHINE]\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
  • Delete the profile which is failing usually has a .bak extension
  • Try logging in again
  • Success

Storage I/O Control

June 12, 2012 Storage, VMware No comments

What is Storage I/ Control?

*VMware Enterprise Plus License Feature

Set an equal baseline and then define priority access to storage resources according to established business rules. Storage I/O Control enables a pre-programmed response to occur when access to a storage resource becomes contentious

With VMware Storage I/O Control, you can configure rules and policies to specify the business priority of each VM. When I/O congestion is detected, Storage I/O Control dynamically allocates the available I/O resources to VMs according to your rules, enabling you to:

  • Improve service levels for critical applications
  • Virtualize more types of workloads, including I/O-intensive business-critical applications
  • Ensure that each cloud tenant gets their fair share of I/O resources
  • Increase administrator productivity by reducing amount of active performance management required.
  • Increase flexibility and agility of your infrastructure by reducing your need for storage volumes dedicated to a single application

How is it configured?

It’s quite straight forward to do. First you have to enable it on the datastores. Only if you want to prioritize a certain VM’s I/Os do you need to do additional configuration steps such as setting shares on a per VM basis. Yes, this can be a bit tedious if you have very many VMs that you want to change from the default shares value. But this only needs to be done once, and after that SIOC is up and running without any additional tweaking needed

The shares mechanism is triggered when the latency to a particular datastore rises above the pre-defined latency threshold seen earlier. Note that the latency is calculated cluster-wide. Storage I/O Control also allows one to tune &  place a maximum on the number of IOPS that a particular VM can generate  to a shared datastore. The Shares and IOPS values are configured on a per VM basis. Edit the Settings of the VM, select the Resource tab, and the Disk setting will allow you to set the Shares value for when contention arises (set to Normal/1000 by default), and limit the IOPs that the VM can generate on the datastore (set to Unlimited by default):

Why enable it?

The thing is, without SIOC, you could definitely hit this noisy neighbour problem where one VM could use more than its fair share of resources and impact other VMs residing on the same datastore. So by simply enabling SIOC on that datastore, the algorithms will ensure fairness across all VMs sharing the same datastore as they will all have the same number of shares by default. This is a great reason for admins to use this feature when it is available to them. And another cool feature is that once SIOC is enabled, there are additional performance counters available to you which you typically don’t have

What threshold should you set?

30ms is an appropriate threshold for most applications however you may want to have a discussion with your storage array vendor, as they often make recommendations around latency threshold values for SIOC

Problems

One reason that this can occur is when the back-end disks/spindles have other LUNs built on them, and these LUNs are presented to non ESXi hosts. Check out

KB 1020651 for details on how to address this and previous posts

and

http://www.electricmonk.org.uk/2012/04/20/external-io-workload-detected-on-shared-datastore-running-storage-io-control-sioc/

Setting up Network Load Balancing (2008 R2)

June 11, 2012 microsoft, NLB No comments

scales

For this post, I built 2 Test Virtual Machines called DACVNLB001 and DACVNLB002 to test setting up Network Load Balancing. These VMs are running Windows Server 2008 R2

  • Once your VMs are built, go into Server Manager or Initial Configuration Tasks and Click Add Features
  • Select Network Load Balancing > Next > Install (On Both Servers)
  • Reboot
  • Open Network Load Balancing Manager on the first server

  • Right click Network Load Balancing Clusters and choose New Cluster. Put in the first server name

  •  Click Connect
  • Click Next

  • Priority is set to 1 because this is a new cluster and this is the first host in the cluster
  • Click Next. We are now on the Cluster IP Address Page. This must be a unique IP Address in the same network as the 2 NLB Nodes

  • Click OK and Next
  • Put a full internet name in and choose cluster operation node as Unicast (More described later on this

  • Click Finish on Port Rules

  • You should now see the below screen

  •  Now we need to add the other host so right click your cluster name/IP Address in this case 10.1.1.190 and select Add Host to Cluster

  •  Type in the 2nd node name

  • Click Connect
  •  Check the screen below is correct and click Next

  •  Click Next on the Ports screen

  • Wait for them to converge

  • You are Complete and should look like the below

 Unicast and Multicast

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

All cluster hosts in a cluster receive all incoming client requests that are destined for the virtual IP address that is assigned to the cluster. The Network Load Balancing load-balancing algorithm, which runs on each cluster host, is responsible for determining which cluster host processes and responds to the client request.

You can distribute incoming client requests to cluster hosts by using unicast or multicast methods. Both methods send the incoming client requests to all hosts by sending the request to the cluster’s MAC address.

When you use the unicast method, all cluster hosts share an identical unicast MAC address. Network Load Balancing overwrites the original MAC address of the cluster adapter with the unicast MAC address that is assigned to all the cluster hosts.

When you use the multicast method, each cluster host retains the original MAC address of the adapter. In addition to the original MAC address of the adapter, the adapter is assigned a multicast MAC address, which is shared by all cluster hosts. The incoming client requests are sent to all cluster hosts by using the multicast MAC address.

Select the unicast method for distributing client requests, unless only one network adapter is installed in each cluster host and the cluster hosts must communicate with each other. Because Network Load Balancing modifies the MAC address of all cluster hosts to be identical, cluster hosts cannot communicate directly with one another when using unicast. When peer-to-peer communication is required between cluster hosts, include an additional network adapter or select multicast mode. When the unicast method is inappropriate, select the multicast method

Selecting the Unicast Method

  • The cluster adapters for all cluster hosts are assigned the same unicast MAC address.
  • The outgoing MAC address for each packet is modified, based on the cluster host’s priority setting, to prevent upstream switches from discovering that all cluster hosts have the same MAC address.
  • The modification of the outgoing MAC address is appropriate for switches. When a hub is used to connect the cluster hosts, disable the modification of the outgoing MAC address. On Windows Server 2003, you can disable modification of outgoing addresses by setting the value of the registry entry MaskSourceMAC, of data type REG_DWORD, to 0x0. MaskSourceMAC is located in HKLM\SYSTEM\CurrentControlSet\Services\WLBS\Parameters\Interface\Adapter-GUID (where Adapter-GUID is the long GUID assigned to the network adapter in the server).
  • The unicast MAC address is derived from the cluster’s IP address to ensure uniqueness outside the cluster hosts.
  • Communication between cluster hosts, other than Network Load Balancing–related traffic (such as heartbeat), is only available when you install an additional adapter, because the cluster hosts all have the same MAC address.

Although the unicast method works in all routing situations, it has the following disadvantages:

  • A second network adapter is required to provide peer-to-peer communication between cluster hosts.
  • If the cluster is connected to a switch, incoming packets are sent to all the ports on the switch, which can cause switch flooding.

Selecting the Multicast Method

  • The cluster adapter for each cluster host retains the original hardware unicast MAC address (as specified by the hardware manufacture of the network adapter).
  • The cluster adapters for all cluster hosts are assigned a multicast MAC address.
  • The multicast MAC is derived from the cluster’s IP address.
  • Communication between cluster hosts is not affected, because each cluster host retains a unique MAC address

By using the multicast method with Internet Group Membership Protocol (IGMP), you can limit switch flooding, if the switch supports IGMP snooping. IGMP snooping allows the switch to examine the contents of multicast packets and associate a port with a multicast address. Without IGMP snooping, switches might require additional configuration to tell the switch which ports to use for the multicast traffic. Otherwise, switch flooding occurs, as with the unicast method.

The multicast method has the following disadvantages:

  • Upstream routers might require a static Address Resolution Protocol (ARP) entry. This is because routers might not accept an ARP response that resolves unicast IP addresses to multicast MAC addresses.
  • Without IGMP, switches might require additional configuration to tell the switch which ports to use for the multicast traffic.
  • Upstream routers might not support mapping a unicast IP address (the cluster IP address) with a multicast MAC address. In these situations, you must upgrade or replace the router. Otherwise, the multicast method is unusable.

Raspberry Pi

June 7, 2012 Technology No comments

What is it?

An ARM GNU/Linux box for $25 Take a Byte! The Raspberry Pi is a credit-card sized computer that plugs into your TV and a keyboard. It’s a capable little PC which can be used for many of the things that your desktop PC does, like spreadsheets, word-processing and games. It also plays high-definition video. They want to see it being used by kids all over the world to learn programming

http://www.raspberrypi.org/faqs

 

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