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Disk I/O Counters

Performance counters are modeled using the PerfCounterInfo data object type. Each instance of a PerfCounterInfo data object contains metadata about a specific metric available from the system. The disk group of counters support metrics for I/O (input/output) performance (such as latency and read- and write-speeds), and utilization metrics for storage as a finite resource. This page includes documentation for disk I/O performance counters only. See Storage Utilization Counters page for information about storage capacity counters.

Disk-I/O counters support metrics for both physical devices and virtual devices:

  • A host reads data from a LUN (logical unit number) associated with the physical storage media.
  • A virtual machine reads data from a virtual disk, which is the virtual hardware presented to the Guest OS running on the virtual machine. The virtual disk is a file in VMDK format.

Some of the counters listed in this table subsume other counters. For example, kernelLatency includes both queueReadLatency and queueWriteLatency. The usage stats include both read and write statistics.

Counter StatsType Unit Level Per
Device
Level		 RollupType Label Entity Instance/
Aggregate		 ESX
Versions
busResets deltanumber23summation Bus resets VirtualMachine
HostSystem
Datastore		instance5.0
5.1
5.5
6.0
6.5
6.7
Number of SCSI-bus reset commands issued during the collection interval
capacity.contention absolutepercent44average Storage Capacity Contention Datastoreaggregate5.0
5.1
5.5
6.0
6.5
6.7
The amount of storage capacity overcommitment for the entity, measured in percent.
capacity.provisioned absolutekiloBytes44average Storage Capacity Provisioned Datastoreaggregate5.0
5.1
5.5
6.0
6.5
6.7
Provisioned size of the entity:
  • Virtual disk: The maximum capacity size of the virtual disk.
  • Virtual machine: The provisioned size of all virtual disks plus snapshot files and the swap file, if the VM is running.
  • Datastore: The maximum capacity of the datastore.
  • POD: The maximum capacity of all datastores in the POD.
capacity.usage absolutekiloBytes44average Storage Capacity Usage Datastoreinstance5.0
5.1
5.5
6.0
6.5
6.7
The amount of storage capacity currently being consumed by or on the entity.
commands deltanumber23summation Commands issued VirtualMachine
HostSystem		instance5.0
5.1
5.5
6.0
6.5
6.7
Number of SCSI commands issued during the collection interval
commandsAborted deltanumber23summation Commands aborted VirtualMachine
HostSystem		instance5.0
5.1
5.5
6.0
6.5
6.7
Number of SCSI commands aborted during the collection interval
commandsAveraged ratenumber23average Average commands issued per second VirtualMachine
HostSystem		instance5.0
5.1
5.5
6.0
6.5
6.7
Average number of SCSI commands issued per second during the collection interval
deltaused absolutekiloBytes23latest Overhead due to delta disk backings
Storage overhead of a virtual machine or a datastore due to delta disk backings
deviceLatency absolutemillisecond13average Physical device command latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time, in milliseconds, to complete a SCSI command from the physical device
deviceReadLatency absolutemillisecond23average Physical device read latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time, in milliseconds, to read from the physical device
deviceWriteLatency absolutemillisecond23average Physical device write latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time, in milliseconds, to write to the physical device
kernelLatency absolutemillisecond23average Kernel command latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time, in milliseconds, spent by VMkernel to process each SCSI command
kernelReadLatency absolutemillisecond23average Kernel read latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time, in milliseconds, spent by VMkernel to process each SCSI read command
kernelWriteLatency absolutemillisecond23average Kernel write latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time, in milliseconds, spent by VMkernel to process each SCSI write command
maxQueueDepth absolutenumber13average Maximum queue depth HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Maximum queue depth.
maxTotalLatency absolutemillisecond13latest Highest latency VirtualMachine
HostSystem		aggregate5.0
5.1
5.5
6.0
6.5
6.7
Highest latency value across all disks used by the host. Latency measures the time taken to process a SCSI command issued by the guest OS to the virtual machine. The kernel latency is the time VMkernel takes to process an IO request. The device latency is the time it takes the hardware to handle the request.
numberRead deltanumber33summation Read requests VirtualMachine
HostSystem		instance5.0
5.1
5.5
6.0
6.5
6.7
Number of disk reads during the collection interval.
  • VM - Number of times data was read from each virtual disk on the virtual machine.
  • Host - Number of times data was read from each LUN on the host.
numberReadAveraged ratenumber13average Average read requests per second VirtualMachine
HostSystem
Datastore		aggregate5.0
5.1
5.5
6.0
6.5
6.7
Average number of read commands issued per second to the datastore during the collection interval.
numberWrite deltanumber33summation Write requests VirtualMachine
HostSystem		instance5.0
5.1
5.5
6.0
6.5
6.7
Number of disk writes during the collection interval.
  • VM - Number of times data was written to each virtual disk on the virtual machine.
  • Host - Number of times data was written to each LUN on the host.
numberWriteAveraged ratenumber13average Average write requests per second VirtualMachine
HostSystem
Datastore		aggregate5.0
5.1
5.5
6.0
6.5
6.7
Average number of write commands issued per second to the datastore during the collection interval.
queueLatency absolutemillisecond23average Queue command latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time spent in the VMkernel queue, per SCSI command, during the collection interval.
queueReadLatency absolutemillisecond23average Queue read latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time spent in the VMkernel queue, per SCSI read command, during the collection interval
queueWriteLatency absolutemillisecond23average Queue write latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time spent in the VMkernel queue, per SCSI write command, during the collection interval
read ratekiloBytesPerSecond23average Read rate VirtualMachine
HostSystem		instance5.0
5.1
5.5
6.0
6.5
6.7
Average number of kilobytes read from the disk each second during the collection interval.
  • VM - Rate at which data is read from each virtual disk on the virtual machine.
  • Host - Rate at which data is read from each LUN on the host.
read rate = # blocksRead per second x blockSize
scsiReservationCnflctsPct absolutepercent44average Disk SCSI Reservation Conflicts %
Number of SCSI reservation conflicts for the LUN as a percent of total commands during the collection interval
scsiReservationConflicts deltanumber22summation Disk SCSI Reservation Conflicts
Number of SCSI reservation conflicts for the LUN during the collection interval
throughput.contention absolutemillisecond44average Disk Throughput Contention ResourcePoolaggregate5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time for an I/O operation to complete successfully
throughput.usage ratekiloBytesPerSecond44average Disk Throughput Usage ResourcePoolaggregate5.0
5.1
5.5
6.0
6.5
6.7
Aggregated disk I/O rate, including the rates for all virtual machines running on the host during the collection interval
totalLatency absolutemillisecond33average Command latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time taken during the collection interval to process a SCSI command issued by the guest OS to the virtual machine.
totalReadLatency absolutemillisecond23average Read latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time taken during the collection interval to process a SCSI read command issued from the guest OS to the virtual machine
totalWriteLatency absolutemillisecond23average Write latency HostSysteminstance5.0
5.1
5.5
6.0
6.5
6.7
Average amount of time taken during the collection interval to process a SCSI write command issued by the guest OS to the virtual machine
usage ratekiloBytesPerSecond1 (4)4average
(minimum)
(maximum)
(none)		 Usage VirtualMachine
HostSystem		aggregate5.5
6.0
6.5
6.7
Aggregated disk I/O rate. For hosts, this metric includes the rates for all virtual machines running on the host during the collection interval.
write ratekiloBytesPerSecond23average Write rate VirtualMachine
HostSystem		instance5.0
5.1
5.5
6.0
6.5
6.7
Average number of kilobytes written to disk each second during the collection interval.
  • VM - Rate at which data is written to each virtual disk on the virtual machine.
  • Host - Rate at which data is written to each LUN on the host.
write rate = # blocksRead per second x blockSize

 

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