VM Snapshots Test

A disk snapshot is a copy of the virtual machine (VM) disk file recorded at a specific time, much like a Windows restore point. The snapshot preserves the original VM disk file by disabling writes to the original disk file - all new writes are made to the snapshot version of the VM. If you create more than one snapshot of your virtual machine (VM), then you’ll have multiple restore points available to revert to. When you create a snapshot, what was currently writable becomes read-only from that point on. Using in-file delta technology, new files are created that contain all changes (delta) to the original disk files.

The size of a snapshot file can never exceed the size of the original disk file. When requests are made to change a block on the original disk, it is instead changed in the delta file. If the previously changed disk block in a delta file is changed again it will not increase the size of the delta file because it simply updates the existing block in the delta file.

Though snapshot files are small in size initially, they will grow as writes are made to the VM’s disk files. If the number and size of the snapshot files grow significantly over time, they might end up eroding considerable datastore space, thereby choking VM operations. To conserve disk space, administrators need to continuously track snapshot growth per VM, identify ‘heavy-weight’ snapshots that may not be of use any longer, and purge them. The VM Snapshots test helps administrators achieve the same. While the measures reported by the test capture the snapshot file count per VM and the total size of the snapshot files of a VM, the detailed diagnosis reveals the size of each snapshot, thus enabling administrators to quickly spot those snapshot files that are too large in size.

Target of the test : An ESX server host

Agent deploying the test : An internal/remote agent

Outputs of the test : One set of results for each VM configured on the ESX host being monitored.

Configurable parameters for the test:
Parameter	Description
Test Period	How often should the test be executed
Host	The host for which the test is to be configured
Port	The port at which the specified HOST listens. By default, this is NULL.
ESX User and ESX Password	In order to enable the test to extract the desired metrics from a target ESX server, you need to configure the test with an ESX USER and ESX PASSWORD. The user credentials to be passed here depend upon the mechanism used by the eG agent for auto-discovering the VMs on the target vSphere server and monitoring the server and its VMs. These discovery/monitoring methodologies and their corresponding configuration requirements have been discussed hereunder: Discovering and monitoring by directly connecting to the target vSphere server: Starting with ESX server 3.0, a VMware ESX server offers a web service interface using which the eG agent discovers the guest operating systems on a physical ESX host. The VMware VI SDK is used by the agent to implement the web services interface. To use this interface for discovering the VMs and for monitoring, the eG agent should directly connect to the monitored vSphere/ESX server as an ESX USER with root privileges. However, if, owing to security constraints, you cannot use root user permissions, you can alternatively configure the tests with the credentials of a user who has been assigned the following permissions: Diagnostics TerminateSession To see how you can create such a user on the ESX server, refer to theCreating a Special Role on an ESX Server and Assigning the Role to a New User topic Discovering and monitoring using vCenter: By default, the eG agent connects to each ESX server and discovers the VMs executing on it. While this approach scales well, it requires additional configuration for each server being monitored. For example, separate user accounts may need to be created on each server for accessing VM details. While monitoring large virtualized installations however, the agents can be optionally configured to perform guest discovery using the VM information already available in vCenter. The same vCenter can also be used to monitor the vSphere server and its VMs. In this case therefore, the ESX USER and ESX PASSWORD that you specify should be that of an Administrator or Virtual Machine Administrator in vCenter. However, if, owing to security constraints, you prefer not to use the credentials of such users, then, you can create a special role on vCenter with the following privileges: Diagnostics Change settings View and stop sessions To know how to grant the above-mentioned permissions to a vCenter user, refer to Creating a Special Role on vCenter and Assigning the Role to a New User . If the ESX server for which this test is being configured had been discovered via vCenter, then the eG manager automatically populates the ESX USERand ESX PASSWORD text boxes with the vCenter user credentials using which the ESX discovery was performed.
Confirm Password	Confirm the specified ESX PASSWORD by retyping it here.
SSL	By default, the ESX server is SSL-enabled. Accordingly, the SSL flag is set to Yes by default. This indicates that the eG agent will communicate with the ESX server via HTTPS by default. On the other hand, if the eG agent has been configured to use the VMPerl API or CLI for monitoring (i.e., if the ESX USER parameter is set to none), then the status of the SSL flag is irrelevant. Like the ESX sever, the vCenter is also SSL-enabled by default. If you have chosen to use the vCenter for monitoring all the ESX servers in your environment, then you have to set the SSL flag to Yes.
Webport	By default, in most virtualized environments, the ESX server and vCenter listen on port 80 (if not SSL-enabled) or on port 443 (if SSL-enabled). This implies that while monitoring an SSL-enabled ESX server directly, the eG agent, by default, connects to port 443 of the ESX server to pull out metrics, and while monitoring a non-SSL-enabled ESX server, the eG agent connects to port 80. Similarly, while monitoring an ESX server via an SSL-enabled vCenter, the eG agent connects to port 443 of vCenter to pull out the metrics, and while monitoring via a non-SSL-enabled vCenter, the eG agent connects to port 80 of vCenter. Accordingly, the WEBPORT parameter is set to 80 or 443 depending upon the status of the SSL flag. In some environments however, the default ports 80 or 443 might not apply. In such a case, against the WEBPORT parameter, you can specify the exact port at which the ESX server or vCenter in your environment listens so that the eG agent communicates with that port.
Virtual Center	If the eG manager had discovered the target ESX server by connecting to vCenter, then the IP address of the vCenter server used for discovering this ESX server would be automatically displayed against the VIRTUAL CENTER parameter; similarly, the ESX USER and ESX PASSWORD text boxes will be automatically populated with the vCenter user credentials, using which ESX discovery was performed. If this ESX server has not been discovered using vCenter, but you still want to discover the guests on the ESX server via vCenter, then select the IP address of the vCenter host that you wish to use for guest discovery from the VIRTUAL CENTER list. By default, this list is populated with the IP address of all vCenter hosts that were added to the eG Enterprise system at the time of discovery. Upon selection, the ESX USERand ESX PASSWORD that were pre-configured for that vCenter server will be automatically displayed against the respective text boxes. On the other hand, if the IP address of the vCenter server of interest to you is not available in the list, then, you can add the details of the vCenter server on-the-fly, by selecting the Other option from the VIRTUAL CENTER list. This will invoke the ADD VCENTER SERVER DETAILS page. Refer to Adding the Details of a vCenter Server for VM Discoverysection to know how to add a vCenter server using this page. Once the vCenter server is added, its IP address, ESX USER, and ESX PASSWORD will be displayed against the corresponding text boxes. On the other hand, if you want the eG agent to behave in the default manner -i.e., communicate with each ESX server for monitoring and VM information - then set the VIRTUAL CENTER parameter to ‘none’.
Inside view using	By default, this test obtains the “inside view” of VMs using the eG VM Agent. Accordingly, the inside view using flag to eG VM Agent by default. The eG VM Agent is a piece of software, which should be installed on every VM on a hypervisor. Every time the eG agent runs this test, it uses the eG VM Agent to pull relevant 'inside view' metrics from each VM. Once the metrics are collected, the eG agent then communicates with each VM agent and pulls these metrics, without requiring administrator privileges. Refer to Configuring the Remote Agent to Obtain the Inside View of VMs for more details on the eG VM Agent.
Exclude VMs	Administrators of some virtualized environments may not want to monitor some of their less-critical VMs - for instance, VM templates - both from ‘outside’ and from ‘inside’. The eG agent in this case can be configured to completely exclude such VMs from its monitoring purview. To achieve this, provide a comma-separated list of VMs to be excluded from monitoring in the EXCLUDE VMS text box. Instead of VMs, VM name patterns can also be provided here in a comma-separated list. For example, your exclude vms specification can be: xp,lin,win,vista. Here, the * (asterisk) is used to denote leading and trailing spaces (as the case may be). By default, this parameter is set to none indicating that the eG agent obtains the inside and outside views of all VMs on a virtual host by default. By providing a comma-separated list of VMs/VM name patterns in the EXCLUDE VMS text box, you can make sure the eG agent stops collecting ‘inside’ and ‘outside’ view metrics for a configured set of VMs.
Ignore VMs Inside View	Administrators of some high security VMware environments might not have permissions to internally monitor one/more VMs. The eG agent can be configured to not obtain the ‘inside view’ of such ‘inaccessible’ VMs using the IGNORE VMS INSIDE VIEW parameter. Against this parameter, you can provide a comma-separated list of VM names, or VM name patterns, for which the inside view need not be obtained. For instance, your IGNORE VMS INSIDE VIEW specification can be: xp,lin,win,vista. Here, the * (asterisk) is used to denote leading and trailing spaces (as the case may be). By default, this parameter is set to none indicating that the eG agent obtains the inside view of all VMs on an ESX host by default. Note: While performing VM discovery, the eG agent will not discover the operating system of the VMs configured in the IGNORE VMS INSIDE VIEW text box.
Ignore WINNT	By default, the eG agent does not support the inside view for VMs executing on Windows NT operating systems. Accordingly, the IGNORE WINNT flag is set to Yes by default.
Age Limit	By default, 15 days is set as AGELIMIT. This implies that the test will report all those snapshots that are more than 15 days old as Old snapshots. If required, you can change the AGELIMIT.
Size Limit	By default, 10000 KB is set as the SIZELIMIT. This implies that the test will report all those snapshots that have a size more than 10000 KB as Large snapshots. If required, you can change the SIZELIMIT.
Show Top	By default, the detailed diagnosis of this test lists the top-10 snapshots in terms of their age and/or size. This is why, the SHOW TOP parameter is set to 10 by default. If you want the detailed diagnosis of this test to list more or less number of snapshots in terms of their age and/or size, then you can change the value of this parameter accordingly.
Detailed Diagnosis	To make diagnosis more efficient and accurate, eG Enterprise embeds an optional detailed diagnostic capability. With this capability, the eG agents can be configured to run detailed, more elaborate tests as and when specific problems are detected. To enable the detailed diagnosis capability of this test for a particular server, choose the On option. To disable the capability, click on the Off option. The option to selectively enable/disable the detailed diagnosis capability will be available only if the following conditions are fulfilled: The eG manager license should allow the detailed diagnosis capability Both the normal and abnormal frequencies configured for the detailed diagnosis measures should not be 0.

Measurements made by the test
Measurement	Description	Measurement Unit	Interpretation
Number of snapshots:	Indicates the number of snapshot files of this VM that are currently available.	Number	A number of snapshots of a VM provides administrators with multiple restore points. On the flipside though, a high number of snapshots can also be considered a waste of valuable disk space, especially if many of the snapshots hold less critical, but heavy-weight changes/writes to the disk. To accurately identify those snapshots that are consuming disk space excessively, and to learn when they were created, who their parents are, and their current consistent file system state, use the detailed diagnosis of this measure.
Total size of snapshots:	Indicates the total size of all snapshots of a VM.	MB	Snapshots typically grow in 16 MB increments to help reduce SCSI reservation conflicts. Though small in size initially (16 MB), snapshots can grow with time, but can never grow beyond the original disk file size. If a marked increase is noticed in the value of this measure over time, it could indicate that one/more snapshots are rapidly growing in size. To know which snapshots are contributing to this phenomenon, use the detailed diagnosis of the Number of snapshots measure. The rate of growth of a snapshot will be determined by how much disk write activity occurs on your server. Servers that have disk write intensive applications, such as SQL and Exchange, will have their snapshot files grow rapidly. On the other hand, servers with mostly static content and fewer disk writes, such as Web and application servers, will grow at a much slower rate.
Large size snapshots count:	Indicates the number of snapshots that are of a size more than the configured SIZELIMIT.	Number	Snapshots typically grow in 16 MB increments to help reduce SCSI reservation conflicts. Though small in size initially (16 MB), snapshots can grow with time, but can never grow beyond the original disk file size. If a marked increase is noticed in the value of this measure over time, it could indicate that a number of snapshots are rapidly growing in size. To know which snapshots are growing beyond the size limit set, use the detailed diagnosis of this measure.
Aged snapshots count:	Indicates the number of snapshots that are of an age over the configured AGELIMIT.	Number	Use the detailed diagnosis of this measure to identify the old snapshots, so that you can figure out whether they deserve to be retained or not. While many snapshots provide essential restore points for VMs, many others hold less critical information. The ‘less useful’ snapshots can be eliminated to save disk space.