1.4.5 Monitoring disk resources

(1) Overview

In a VMware system, multiple virtual machines share the physical server's physical disk. The physical disk space is logically partitioned into logical disks, which are then allocated to individual virtual machines. The OS running on a virtual machine recognizes an allocated logical disk as a normal physical disk.

The following two types of disk resources are available:

• Disk I/O resource

  This is a resource related to disk access statuses.

• Disk space resource

  This is a resource related to disk space.

Since the physical disk is shared in a virtual environment, it is accessed by the individual virtual machines simultaneously. If multiple disk commands are issued simultaneously, the disk I/O resource is distributed according to share ratios that have been set up by the virtual environment software.

Disk commands from a virtual machine for which a large share ratio is set are executed at higher priority. Consequently, disk commands from a virtual machine with a small share ratio may be discarded without being executed. Discarded disk commands are re-executed after a time.

If the rate at which commands are discarded becomes high, disk access is delayed, adversely affecting the performance of the virtual machine. By monitoring the performance data of the disk I/O resource, you can detect such performance deterioration of the virtual machine, and you can thus take the necessary corrective action.

Furthermore, you can check whether there is a logical disk space insufficiency by monitoring the performance data of the disk space resource.

The four records described below are used to monitor the disk resource. For details about records, see 5. Records.

1. PI_HPDI record

   This record is used to monitor the performance data of the physical disk. It shows the disk I/O resource as viewed from the physical server.

2. PI_VPDI record

   This record is used to monitor the performance data of the physical disk being used by the virtual machine. It shows the disk I/O resource as viewed from the virtual machine.

3. PI_HLDI record

   This record is used to monitor the performance data of the physical server's logical disk. It shows the disk space resource as viewed from the physical server.

4. PI_VLDI record

   This record is used to monitor the performance data of the virtual machine's logical disk. It shows the disk space resource as viewed from the virtual machine.

The figure below shows the range of performance data collected in each record.

Figure 1‒19: Correspondence between records and data collection ranges

Important note

This note pertains to the source data for the record that JP1/PFM - RM for VM uses to monitor the VMware data store (Used, Free, and Used % fields of the PI_HLDI record). The source data is equivalent to the amount of free space displayed for the storage on the Configuration page when the connection-destination VMware ESX is displayed in vSphere Client.^#

#

This value might be different from the amount of free space displayed in vSphere Client that is connected to vCenter Server. If vSphere Client is connected to vCenter Server, recheck the value by connecting to VMware ESX.

This value is updated every 30 minutes if both of the following conditions are satisfied:

• ESX (or ESXi) is managed with vCenter.

• Virtual machines using VMFS volumes (inactive volumes) are running.

If both of the above conditions are not satisfied, the amount of free space is not updated. The values of the Used, Free, and Used % fields of the PI_HLDI record acquired by JP1/PFM - RM for VM are not updated, either.

To collect or monitor the data of the Used, Free, and Used % fields of the PI_HLDI record, make sure that the system configuration satisfies the above two conditions. In addition, connect vSphere Client to monitoring-target VMware ESX, and then confirm that the last update time displayed for the storage on the Configuration page is updated every 30 minutes. If this time is not updated even if the system configuration satisfies the above two conditions, contact the VMware support center.

Note that, even if the above conditions are satisfied, the amount of free space might not be updated due to a KB2008367 problem with VMware (see below).

For further information about countermeasures or other topics, contact VMware.

KB2008367: Amount of free space reported on the host is incorrect in vCenter Server

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(2) Monitoring examples

Using monitoring of disk resources for vhost1 and vhost2 running on a physical server called host1 as an example, this subsection explains the problems that might occur in the disk resources and how to solve them. The following figure shows the items monitored here, and the flow of actions to take.

Figure 1‒20: Monitored items and flow of actions

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(3) Other monitoring examples

Monitoring examples follow that use monitoring templates other than those explained in (2) Monitoring examples.

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