Storage LUNs – ESX Test

LUN is a Logical Unit Number. It can be used to refer to an entire physical disk, or a subset of a larger physical disk or disk volume. The physical disk or disk volume could be an entire single disk drive, a partition (subset) of a single disk drive, or disk volume from a RAID controller comprising multiple disk drives aggregated together for larger capacity and redundancy.

The Storage LUNs – ESX test reports critical usage statistics pertaining to every LUN on the ESX server host. In the VMware environment, a LUN is typically referred to using its HBA path, where HBA stands for the Host Bus Adapter. The HBA path on the other hand is expressed using the notation: vmhba<HBA  ID:Target ID:LUN ID>. For example, if the HBA path is vmhba0:0:0, then the first 0 indicates the HBA ID, the second zero represents the Target ID, and the final 0 the LUN ID.  

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 LUN on the ESX server host that is 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 WEBPORTparameter 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 WEBPORTparameter, 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’.

Report DD IOPS Value Above

To conserve the space on the database, this test allows you to generate the detailed diagnostics of the Total IOPS measure, ony if the value of the Total IOPS measure is greater than or equal to 100, by default. However, you can override this setting if necessary.

Report DD Throughput Value Above

To conserve the space on the database, this test allows you to generate the detailed diagnostics of the Throughput measure, only if the value of the Throughput measure is greater than or equal to 5. However, you can override this setting if necessary.

Rep DD For Multi-path

The detailed diagnostics of the Number of multi paths available to a LUN measure lists all the paths using which hosts communicate with a LUN. A single LUN may be associated with multiple paths. In large virtualized infrastructures therefore, the detailed diagnostics may report numerous paths. This will not only clutter your view, but will also consume excessive database space. To avoid this, detailed metrics are not reported for the Number of multi paths available to a LUN measure, by default. Accordingly, this flag is set to No by default. If you want detailed diagnosis to be reported for the Number of multi paths available to a LUN measure, then set this flag to Yes.

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

Total device IOPS

Indicates the rate at which commands were issued to this LUN.

Commands/Sec

Use the detailed diagnosis of this measure to know the rate at which commands were issued by each VM that is using the LUN.

Physical disk reads

Indicates the rate at which read commands were issued.

Commands/Sec

 

Physical disk writes

Indicates the rate at which write commands were issued.

Commands/Sec

 

Issued commands

Indicates the number of commands issued per second.

Commands/Sec

 

Physical disk commands aborted

Indicates the number of commands aborted per second.

Aborts/Sec

 

Data writes to physical disk

Indicates the rate at which data was written.

MB/Sec

Use the detailed diagnosis of this measure to know the rate at which data each VM is is writing data.

Data reads from physical disk

Indicates the rate at which data was read.

MB/Sec

Use the detailed diagnosis of this measure to know the rate at which data each VM is reading data.

Bus resets

Indicates the number of SCSI bus resets.

Number

The VMs use the SCSI protocol to communicate to disks, even over Fibre Channel to SAN Luns. SCSI Bus Resets are issued to release resources. These SCSI Bus Resets are in effect the SCSI subsystem timing out, commands being canceled, and retrying. This happens when the HBA device is overloaded, or its q-depth is exhausted. The first thing to know is which vmhba controller©, target/path (T), and LUN (L) experienced these problems. The more VMs sharing a single Lun the more likely that resets will occur. A rule of thumb is no more than 10 VMs sharing a Lun.

Guest read latency

Indicates the average amount of time taken for a read from the perspective of a guest operating system.

Secs

This is the sum of kernel latency and physical device read latency.

High latency is a cause for concern, as it is an indicator of contention for storage resources.

If the value of this measure is high, then check the values reported by the Kernel disk read latency and Physical device read latency measures for this storage adapter. Doing so enables you to quickly determine why exactly the guest OS is experiencing latencies while reading from the disk - is it because of latencies in the VM kernel? Or is it owing to a slowdown in the physical device?

Guest write latency

Indicates the average amount of time taken for a write from the perspective of a guest operating system.

Secs

This is the sum of kernel latency and physical device write latency.

High latency is always a cause for concern, as it is an indicator of contention for storage resources.

If the value of this measure is high, then check the values reported by the Kernel disk write latency and Physical device write latency measures for this storage adapter. Doing so enables you to quickly determine why exactly the guest OS is experiencing latencies while writing to this disk - is it because of latencies in the VM kernel? Or is it owing to a slowdown in the physical device?

Disk command latency

Indicates the average amount of time taken for a command to execute, from the perspective of a guest operating system.

Secs

This is the sum of kernel latency and physical device command latency.

High latency is always a cause for concern, as it is an indicator of contention for storage resources.

If the value of this measure is high, then check the values reported by the Kernel disk command latency and Physical device command latency measures for this storage adapter. Doing so enables you to quickly determine why exactly the guest OS is experiencing latencies while executing commands on this disk - is it because of latencies in the VM kernel? Or is it owing to a slowdown in the physical device?

Kernel disk read latency

Indicates the average time spent in the ESX server’s VM kernel per read.

Secs

A high value for this measure is a cause for concern. You might hence want to investigate the reasons for the same.

Kernel disk write latency

Indicates the average time spent in ESX server VM kernel per write.

Secs

Kernel disk command latency

Indicates the average time spent in the ESX server VM kernel per command.

Secs

Queue read latency

Indicates the average time spent in the ESX server VM kernel queue per read.

Secs

A high value of this measure indicates that the VMkernel is unable to process queued read requests quickly. If the problem persists, then the queue size could increase considerably.

To avoid this, swiftly determine the reasons for a slowdown at the VMkernel, and fix it.

Queue write latency

Indicates the average time spent in the ESX server VM kernel queue per write.

Secs

A high value of this measure indicates that the VMkernel is unable to process queued write requests quickly. If the problem persists, then the queue size could increase considerably.

To avoid this, swiftly determine the reasons for a slowdown at the VMkernel, and fix it.

Queue command latency

Indicates the average time spent in the ESX server VM kernel queue per command.

Secs

A high value of this measure indicates that the VMkernel is unable to process queued commands quickly. If the problem persists, then the queue size could increase considerably.

To avoid this, swiftly determine the reasons for a slowdown at the VMkernel, and fix it.

Physical device read latency

Indicates the average time taken to complete a read from the physical device.

Secs

Shortage of the physical storage resources can adversely impact the performance of the ESX host and the VMs configured on it.

Therefore, if the value of this measure is very high or is steadily increasing, then quickly figure out what is pulling down the performance of the physical disk, and attend to it.

Physical device write latency

Indicates the average time taken to complete a write to the physical device.

Secs

Physical device command latency

Indicates the average time taken to complete a command from the physical device.

Secs

Status

Indicates the current state of this LUN.

 

A LUN can be in any one of the following states:

  • Ok
  • error
  • Off
  • unknownState
  • lostCommunication
  • degraded
  • quiesced

The numeric values that correspond to each of the states discussed above are listed in the table below:

State Value

UnknownState

0

Ok

1

Off

2

Error

3

lostCommunication

4

degraded

5

quiesced

6

Note:

By default, this measure reports the States listed in the table above to indicate the status of a LUN. The graph of this measure however, represents the status of a LUN using the numeric equivalents - 0 to 6.

Number of multi paths available to a LUN

Indicates the number of storage paths through which the host communicates with this LUN.

Number

To maintain a constant connection between an ESX/ESXi host and its storage, ESX/ESXi supports multipathing. Multipathing is a technique that lets you use more than one physical path that transfers data between the host and an external storage device. In case of a failure of any element in the SAN network, such as an adapter, switch, or cable, ESX/ESXi can switch to another physical path, which does not use the failed component. This process of path switching to avoid failed components is known as path failover.

In addition to path failover, multipathing provides load balancing. Load balancing is the process of distributing I/O loads across multiple physical paths. Load balancing reduces or removes potential bottlenecks.

Queue depth

Indicates the number of outstanding I/O requests to this LUN for which a response has not been received from the LUN.

Number

A low value is desired for this measure. A high value is indicative of a large number of pending requests for the LUN and hints at a potential processing bottleneck on the LUN.

Throughput

Indicates the rate at which data was read and written to this LUN.

MB/Sec

A high value is desired for this measure. A consistent decrease in the value of this measure can signal a potential slowdown of the LUN.

Capacity

Indicates the total capacity of this LUN.

MB

 

Capacity used

Indicates the amount of space used in this LUN.

MB

Compare the value of this measure across LUNs to know which LUN is consuming space excessively.

Capacity reserved

Indicates the amount of space reserved for this LUN.

MB

 

Free capacity

Indicates the amount of free space currently available for this LUN.

MB

Compare the value of this measure across LUNs to know which LUN is rapidly running out of space.

Capacity usage

Indicates the percentage of space in this LUN that is in use.

Percent

A low value is desired for this measure. A value close to 100% is a cause for concern, as it indicates a potential space crunch on the LUN. You may want to compare the value of this measure across LUNs to know which LUN is utilizing disk space excessively.

Is SSD?

Indicates whether/not this LUN is SSD or non-SSD.

 

Solid State Disks (SSD) offer a much higher throughput and much lower latency than traditional magnetic hard disks, since they are based on flash memory. vSphere hosts can use locally attached SSDs as a host swap cache, as virtual flash, as a vSAN, or as a regular datastore.

If the LUN being monitored is SSD-based, then the value of this measure wwill be Yes. If not, then the value of this measure will be No.

The numeric values that correspond to each of the measure values listed above are as follows:

Measure value Numeric Value
Yes 1
No 0

Note:

By default, this measure reports the Measure Values listed in the table above. In the graph of this measure however, the SSD status of the LUN is represented using the corresponding numeric equivalents only.

LUN health

Indicates the current health status of this LUN.

 

The values that this measure can report and their corresponding numeric values are discussed in the table above:

Measure Value Numeric Value

Healthy

0

Failed

4

Offline

5

Decommissioned

6

Permanent disk failure

16

Note:

By default, this measure reports the Measure Values listed in the table above. In the graph of this measure however, the health status of the LUN is represented using the corresponding numeric equivalents only.

The detailed diagnosis of the Total device IOPS measure lists the VMs using a storage LUN and the rate at which each VM  is issuing commands to that LUN.

Figure 1 : The detailed diagnosis of the Total device IOPS measure

The detailed diagnosis of the Data reads from physical disk measure reveals the rate at which each VM is reading data from physical disk.

Figure 2 : The detailed diagnosis of the Data reads from physical disk measure

The detailed diagnosis of the Data writes to physical disk measure reveals the rate at which each VM is writing data to physical disk.

Figure 3 : The detailed diagnosis of the Data writes to physical disk measure