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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 | delta | number | 2 | 3 | summation | Bus resets | VirtualMachine HostSystem Datastore | instance | 5.0 5.1 5.5 6.0 6.5 6.7
Number of SCSI-bus reset commands issued during the collection interval
capacity.contention | absolute | percent | 4 | 4 | average | Storage Capacity Contention | Datastore | aggregate | 5.0 5.1 5.5 6.0 6.5 6.7
The amount of storage capacity overcommitment for the entity, measured in percent.
capacity.provisioned | absolute | kiloBytes | 4 | 4 | average | Storage Capacity Provisioned | Datastore | aggregate | 5.0 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 | absolute | kiloBytes | 4 | 4 | average | Storage Capacity Usage | Datastore | instance | 5.0 5.1 5.5 6.0 6.5 6.7
The amount of storage capacity currently being consumed by or on the entity.
commands | delta | number | 2 | 3 | summation | Commands issued | VirtualMachine HostSystem | instance | 5.0 5.1 5.5 6.0 6.5 6.7
Number of SCSI commands issued during the collection interval
commandsAborted | delta | number | 2 | 3 | summation | Commands aborted | VirtualMachine HostSystem | instance | 5.0 5.1 5.5 6.0 6.5 6.7
Number of SCSI commands aborted during the collection interval
commandsAveraged | rate | number | 2 | 3 | average | Average commands issued per second | VirtualMachine HostSystem | instance | 5.0 5.1 5.5 6.0 6.5 6.7
Average number of SCSI commands issued per second during the collection interval
deltaused | absolute | kiloBytes | 2 | 3 | latest | Overhead due to delta disk backings |  |  |
Storage overhead of a virtual machine or a datastore due to delta disk backings
deviceLatency | absolute | millisecond | 1 | 3 | average | Physical device command latency | HostSystem | instance | 5.0 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 | absolute | millisecond | 2 | 3 | average | Physical device read latency | HostSystem | instance | 5.0 5.1 5.5 6.0 6.5 6.7
Average amount of time, in milliseconds, to read from the physical device
deviceWriteLatency | absolute | millisecond | 2 | 3 | average | Physical device write latency | HostSystem | instance | 5.0 5.1 5.5 6.0 6.5 6.7
Average amount of time, in milliseconds, to write to the physical device
kernelLatency | absolute | millisecond | 2 | 3 | average | Kernel command latency | HostSystem | instance | 5.0 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 | absolute | millisecond | 2 | 3 | average | Kernel read latency | HostSystem | instance | 5.0 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 | absolute | millisecond | 2 | 3 | average | Kernel write latency | HostSystem | instance | 5.0 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 | absolute | number | 1 | 3 | average | Maximum queue depth | HostSystem | instance | 5.0 5.1 5.5 6.0 6.5 6.7
Maximum queue depth.
maxTotalLatency | absolute | millisecond | 1 | 3 | latest | Highest latency | VirtualMachine HostSystem | aggregate | 5.0 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 | delta | number | 3 | 3 | summation | Read requests | VirtualMachine HostSystem | instance | 5.0 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 | rate | number | 1 | 3 | average | Average read requests per second | VirtualMachine HostSystem Datastore | aggregate | 5.0 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 | delta | number | 3 | 3 | summation | Write requests | VirtualMachine HostSystem | instance | 5.0 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 | rate | number | 1 | 3 | average | Average write requests per second | VirtualMachine HostSystem Datastore | aggregate | 5.0 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 | absolute | millisecond | 2 | 3 | average | Queue command latency | HostSystem | instance | 5.0 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 | absolute | millisecond | 2 | 3 | average | Queue read latency | HostSystem | instance | 5.0 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 | absolute | millisecond | 2 | 3 | average | Queue write latency | HostSystem | instance | 5.0 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 | rate | kiloBytesPerSecond | 2 | 3 | average | Read rate | VirtualMachine HostSystem | instance | 5.0 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 | absolute | percent | 4 | 4 | average | Disk SCSI Reservation Conflicts % |  |  |
Number of SCSI reservation conflicts for the LUN as a percent of total commands during the collection interval
scsiReservationConflicts | delta | number | 2 | 2 | summation | Disk SCSI Reservation Conflicts |  |  |
Number of SCSI reservation conflicts for the LUN during the collection interval
throughput.contention | absolute | millisecond | 4 | 4 | average | Disk Throughput Contention | ResourcePool | aggregate | 5.0 5.1 5.5 6.0 6.5 6.7
Average amount of time for an I/O operation to complete successfully
throughput.usage | rate | kiloBytesPerSecond | 4 | 4 | average | Disk Throughput Usage | ResourcePool | aggregate | 5.0 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 | absolute | millisecond | 3 | 3 | average | Command latency | HostSystem | instance | 5.0 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 | absolute | millisecond | 2 | 3 | average | Read latency | HostSystem | instance | 5.0 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 | absolute | millisecond | 2 | 3 | average | Write latency | HostSystem | instance | 5.0 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 | rate | kiloBytesPerSecond | 1 (4) | 4 | average (minimum) (maximum) (none) | Usage | VirtualMachine HostSystem | aggregate | 5.5 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 | rate | kiloBytesPerSecond | 2 | 3 | average | Write rate | VirtualMachine HostSystem | instance | 5.0 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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