eG Monitoring
 

Measures reported by VmgPervDiskTest

The personal vDisk retains the single image management of pooled and streamed desktops while allowing people to install applications and change their desktop settings.

Unlike traditional Virtual Desktop Infrastructure (VDI) deployments involving pooled desktops, where users lose their customizations and personal applications when the administrator alters the base virtual machine (VM), deployments using personal vDisks retain those changes. This means administrators can easily and centrally manage their base VMs while providing users with a customized and personalized desktop experience.

Personal vDisks provide this separation by redirecting all changes made on the user's VM to a separate disk (the personal vDisk) attached to the user's VM. The content of the personal vDisk is blended at runtime with the content from the base VM to provide a unified experience. In this way, users can still access applications provisioned by their administrator in the base VM.

But, what happens if a personal vDisk runs out of space? Simple! Users will no longer be able to hold on to their customizations, allowing them access to only the base VM and the applications installed therein! This outcome beats the entire purpose of having personal vDisks! If this is to be avoided, then administrators should continuously monitor the usage of the personal vDisks, proactively detect a potential space crunch, determine what is causing the rapid erosion of space on the personal vDisk, and fix the root-cause, before desktop users complain. This is where the VmgPervDiskTest test helps.

For each VM on a XenServer, this test tracks the status and space usage of its personal vDisk and promptly reports errors / abnormal space usage. This way, administrators can accurately identify personal vDisks with very limited space, which VM such personal vDisks are associated with, and what is consuming too much disk space - user profiles? Or user applications?

The measures made by this test are as follows:

Measurement Description Measurement Unit Interpretation
Status Indicates whether Citrix Personal vDisk service is running or not on this VM.   The values that this measure can report and their corresponding numeric values have been discussed in the table below:

Measure Value Numeric Value
Stopped 0
Running 1
Not installed 2

Note:

By default, this test reports the Measures Values listed in the table above to indicate the status of the Personal vDisk service. In the graph of this measure however, the same will be represented using the numeric equivalents.
Recomp_status Indicates the status of the initially provisioned disk or the updated image. Number Use the detailed diagnosis of this measure to know for which VM the initial personal vDisk provisioning or image update were unsuccessful and why. The VM can be in one of the following states:

  • OK - The initial provisioning or last image update was successful.
  • Disk Init - This is the first time that the personal vDisk has started or been resized. It is being initialized and partitioned by the service.
  • Disk Format - The personal vDisk is being formatted.
  • Updating - The initial provisioning or an image update is in progress.
  • Error (Disk Discovery) - An error state. An error occurred while discovering the personal vDisk.
  • Error (Disk Init) - An error state. An error occurred while partitioning or formatting the personal vDisk.
  • Error (Sys Init) - An error state. An error occurred while starting the Personal vDisk Service or configuring the personal vDisk.
  • Error (Update) - An error state. An error occurred during the initial provisioning or the last image update.
  • Unknown - An error state. An error occurred but the cause is unknown.
Cur_app_size Indicates the amount of space used by applications installed on the personal vDisk attached to this VM. MB Personal vDisks have two parts, which use different drive letters and are by default equally sized.

One part comprises a Virtual Hard Disk file (a .vhd file). This contains items such as applications installed in C:\Program Files. By default, this part uses drive V: but is hidden from users.

These measures indicate how much space has been allocated to this .vhd file and how much of the allocated space has been utilized by user applications contained in this file.

A high value for the Cur_app_size and App_used measures is indicative of excessive space used by user applications. You can compare the value of these measures across VMs to know which user to which VM has utilized too much space reserved for user applications on the personal vDisk. If the value of the App_used measure grows close to 100% for any VM, it implies that potentially, the user to that VM will not be able to install any applications on the personal vDisk; nor access any applications.

Tot_app_size Indicates the amount of space allocation for storing user applications on the personal vDisk attached to this VM. MB
App_used Indicates the percentage of allocated space used by applications installed on the personal vDisk attached to this VM. Percent
Cur_prof_size Indicates the amount of space used for storing user profiles on the personal vDisk attached to this VM. MB Personal vDisks have two parts, which use different drive letters and are by default equally sized.

One part comprises C:\Users (in Windows 7) or C:\Documents and Settings (in Windows XP). This contains user data, documents, and the user profile. By default this uses drive P:.

These measures indicate how much space has been allocated to user profiles and how much of the allocated space has been utilized by user profiles.

A high value for the Cur_prof_size and Prof_used measures is indicative of excessive space used by user profiles. You can compare the value of these measures across VMs to know which VM's user profiles are consuming the maximum space on the personal vDisk. If the value of the Prof_used measure grows close to 100% for any VM, it implies that potentially, the user to that VM will not be able to store/access any more documents or user data on the personal vDisk.

Tot_prof_size Indicates the amount of space allocated for storing user profiles on the personal vDisk attached to this VM. MB
Prof_used Indicates the percentage of allocated space that has been used up by user profiles on the personal vDisk attached to this VM. Percent
Free_bytes Indicates the amount of unused space on the personal vDisk attached to this VM. MB Ideally, the value of this measure should be high. You can compare the value of this measure across VMs to know which VM's personal vDisk has the least free space. You may then want to resize that personal vDisk to accommodate more data.
Total_bytes Indicates the total size of the personal vDisk attached to this VM. MB The minimum size of a Personal vDisk is 3 GB, however a size of 10 GB is recommended.
Bytes_used Indicates the percentage of space in the personal vDisk attached to this VM that is currently used. Percent A consistent increase in the value of this measure is a cause for concern, as it indicates a gradual erosion of free space in the personal vDisk of a VM.

By comparing the value of this measure across VMs, you can identify which VM's personal vDisk is running out of space! Once the VM with the space-hungry vDisk is isolated, you may want to compare the value of the App_used and Prof_used measures of that VM, to clearly understand what is occupying too much space in the personal vDisk - is it the user profiles? Or is it the user applications? Based on this inference, you can figure out which drive partition of the personal vDisk has limited free space, and can decide between freeing up space in that partition or allocating more space to the personal vDisk itself.