PVS Accelerator - Xen Test

The XenServer PVS-Accelerator feature offers additional capabilities for customers using XenServer and Citrix Provisioning Services (PVS). PVS is a popular choice for image management and hosting for Citrix Virtual Apps and Desktops. PVS-Accelerator employs a Proxy mechanism that resides in the Control Domain (dom0) of the XenServer. When the PVS Accelerator feature is enabled, Citrix Provisioning targets device (VM) read requests are cached directly on the XenServer host. These requests are cached in physical memory or a storage repository. When subsequent VMs on the target XenServer host make the same read requests, the virtual disk is streamed directly from cache, not from the Citrix Provisioning server. This eliminates the need to stream from the Citrix Provisioning server, thereby considerably reducing network utilization and processing on the server and improving the performance of the VM. Hence, monitoring processing of the read requests and network traffic flow from cached PVS server/client is essential for administrators to identify how efficiently the reads are serviced and the traffic flow that used excessive bandwidth. The PVS Accelerator - Xen test can help administrators to continuously track the flow of read requests.

The test reveals the bandwidth usage for processing the read requests from the cache on the target XenServer host and the type of traffic that is causing excessive bandwidth usage, thereby providing pointers to how the PVS client/server configuration can be fine-tuned in order to reduce bandwidth consumption and improve performance.

Target of the test : A XenServer host

Agent deploying the test : An internal/remote agent

Outputs of the test : One set of results for the target XenServer host that is being monitored.

Configurable parameters for the test

  1. Test period - How often should the test be executed.
  2. Host - The host for which the test is to be configured.
  3. XEN user - To enable the eG agent to connect to the XenServer API for collecting statistics of interest, this test should login to the XenServer as a root user. Provide the name of the root user in the XEN USER text box. Root user privileges are mandatory when monitoring a XenServer 5.5 (or below). However, if you are monitoring XenServer 5.6 (or above) and you prefer not to expose the credentials of the root user, then, you have the option of configuring a user with pool-admin privileges as the xen user. If you do not want to expose the credentials of a root/pool-admin user, then you can configure the tests with the credentials of a xen user with Read-only privileges to the XenServer. However, if this is done, then the Xen Uptime test will not run, and the Xen CPU and Xen Memory tests will not be able to report metrics for the control domain descriptor. To avoid such an outcome, do the following before attempting to configure the eG tests with a xen user who has Read-only privileges to the XenServer:

    • Modify the target XenServer’s configuration in the eG Enterprise system. For this, follow the Infrastructure -> Components -> Add/Modify menu sequence, pick Citrix XenServer as the Component type, and click the Modify button corresponding to the target XenServer.
    • In the modify component details page that then appears, make sure that the os is set to Xen and the Mode is set to ssh.
    • Then, in the same page, proceed to provide the User and Password of a user who has the right to connect to the XenServer console via SSH.
    • Then, click the Update button to save the changes.
  4. Once this is done, you can configure the eG tests with the credentials of a xen user with Read-only privileges.   

  5. xen password - The password of the specified xen user needs to be mentioned here.
  6. confirm password - Confirm the xen password by retyping it here.
  7. ssl - By default, the Xen Server is not SSL-enabled. This indicates that by default, the eG agent communicates with the XenServer using HTTP. Accordingly, the ssl flag is set to No by default. If you configure the XenServer to use SSL, then make sure that the SSL flag is set to Yes, so that the eG agent communicates with the XenServer using HTTPS. Note that a default SSL certificate comes bundled with every XenServer installation. If you want the eG agent to use this default certificate for communicating with an SSL-enabled XenServer, then no additional configuration is required. However, if you do not want to use the default certificate, then you can generate a self-signed certificate for use by the XenServer. In such a case, you need to explicitly follow the broad steps given below to enable the eG agent to communicate with the XenServer via HTTPS:

    • Obtain the server-certificate for the XenServer
    • Import the server-certificate into the local certificate store of the eG agent

    For a detailed discussion on each of these steps, refer to the Troubleshooting section of this document.

  8. webport - By default, in most virtualized environments, the XenServer listens on port 80 (if not SSL-enabled) or on port 443 (if SSL-enabled). This implies that while monitoring an SSL-enabled XenServer, the eG agent, by default, connects to port 443 of the server to pull out metrics, and while monitoring a non-SSL-enabled XenServer, the eG agent connects to port 80. 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 XenServer in your environment listens so that the eG agent communicates with that port.
Measurements made by the test
Measurement Description Measurement Unit Interpretation

Eviction rate

Indicates the rate at which the bytes are evicted from the cache on the target Citrix XenServer.

KB/sec

 

Total read

Indicates the total number of reads received by the cache per second.

Reads/sec

 

Read hits

Indicates the number of reads serviced from the cache per second.

Hits/sec

 

Read misses

Indicates the number of reads that cannot be serviced from the cache per second.

Misses/sec

 

Percentage of reads

Indicates the percentage of reads serviced from the cache per second.

Percent

 

Network traffic from client

Indicates the rate which the bytes are transferred from the cached PVS client on the target Citrix XenServer.

KB/sec

 

Network traffic from server

Indicates the rate which the bytes are transferred from the cached PVS server on the target Citrix XenServer.

KB/sec

 

Network traffic saved

Indicates the rate which the bytes are transferred from the PVS Accelerator instead of the PVS server on the target Citrix XenServer.

KB/sec

 

Space utilization

Indicates the percentage of space utilized by the PVS Accelerator compared to the total size of the cache storage on the target XenServer.

Percent