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	RollupType	Label	Entity
Counter	StatsType	Unit	Level	RollupType	Label	V	H	D
busResets	delta	number	2	summation	Disk Bus Resets	•	•	ο
busResets	Number of SCSI-bus reset commands issued during the collection interval.
commands	delta	number	2	summation	Disk Commands Issued	•	•	ο
commands	Number of SCSI commands issued during the collection interval.
commandsAborted	delta	number	2	summation	Disk Command Aborts	•	•	ο
commandsAborted	Number of SCSI commands aborted during the collection interval.
deviceLatency	absolute	millisecond	2	average	Physical Device Command Latency	•	•	ο
deviceLatency	Average amount of time, in milliseconds, to complete a SCSI command from the physical device.
deviceReadLatency	absolute	millisecond	2	average	Physical Device Read Latency	•	•	ο
deviceReadLatency	Average amount of time, in milliseconds, to complete read from the physical device.
deviceWriteLatency	absolute	millisecond	2	average	Physical Device Write Latency	•	•	ο
deviceWriteLatency	Average amount of time, in milliseconds, to write to the physical device (LUN).
kernelLatency	absolute	millisecond	2	average	Kernel Disk Command Latency	•	•	ο
kernelLatency	Average amount of time, in milliseconds, spent by VMkernel processing each SCSI command.
kernelReadLatency	absolute	millisecond	2	average	Kernel Disk Read Latency	•	•	ο
kernelReadLatency	Average amount of time, in milliseconds, spent by VMKernel processing each SCSI read command.
kernelWriteLatency	absolute	millisecond	2	average	Kernel Disk Write Latency	•	•	ο
kernelWriteLatency	Average amount of time, in milliseconds, spent by VMKernel processing each SCSI write command.
maxTotalLatency	absolute	millisecond	3	average	Highest Disk Latency	•	•	ο
maxTotalLatency	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	summation	Disk Read Requests	•	•	ο
numberRead	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.
numberWrite	delta	number	3	summation	Disk Write Requests	•	•	ο
numberWrite	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.
queueLatency	absolute	millisecond	2	average	Queue Command Latency	•	•	ο
queueLatency	Average amount of time spent in the VMkernel queue, per SCSI command, during the collection interval.
queueReadLatency	absolute	millisecond	2	average	Queue Read Latency	•	•	ο
queueReadLatency	Average amount of time taken during the collection interval per SCSI read command in the VMKernel queue.
queueWriteLatency	absolute	millisecond	2	average	Queue Write Latency	•	•	ο
queueWriteLatency	Average amount time taken during the collection interval per SCSI write command in the VMKernel queue.
read	rate	kiloBytesPerSecond	2	average	Disk Read Rate	•	•	ο
read	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
totalLatency	absolute	millisecond	2	average	Disk Command Latency	•	•	ο
totalLatency	Average amount of time taken during the collection interval to process a SCSI command issued by the Guest OS to the virtual machine. The sum of kernelLatency and deviceLatency.
totalReadLatency	absolute	millisecond	2	average	Disk Read Latency	•	•	ο
totalReadLatency	Average amount of time taken during the collection interval to process a SCSI read command issued from the Guest OS to the virtual machine. The sum of kernelReadLatency and deviceReadLatency.
totalWriteLatency	absolute	millisecond	2	average	Disk Write Latency	•	•	ο
totalWriteLatency	Average amount of time taken during the collection interval to process a SCSI write command issued by the Guest OS to the virtual machine. The sum of kernelWriteLatency and deviceWriteLatency.
usage	kiloBytesPerSecond	rate	1 (4)	average (minimum) (maximum) (none)	Disk Usage (Average) Disk Usage (Minimum) Disk Usage (Maximum) Disk Usage (None)	•	•	ο
usage	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	average	Disk Write Rate	•	•	ο
write	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