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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.

Legend:V=VirtualMachine|H=HostSystem|D=Datastore
Counter StatsType Unit Level RollupType Label      Entity
VHD
busResets deltanumber2summationDisk Bus Resetsο
Number of SCSI-bus reset commands issued during the collection interval.
commands deltanumber2summationDisk Commands Issuedο
Number of SCSI commands issued during the collection interval.
commandsAborted deltanumber2summationDisk Command Abortsο
Number of SCSI commands aborted during the collection interval.
deviceLatency absolutemillisecond2averagePhysical Device Command Latencyο
Average amount of time, in milliseconds, to complete a SCSI command from the physical device.
deviceReadLatency absolutemillisecond2averagePhysical Device Read Latencyο
Average amount of time, in milliseconds, to complete read from the physical device.
deviceWriteLatency absolutemillisecond2averagePhysical Device Write Latencyο
Average amount of time, in milliseconds, to write to the physical device (LUN).
kernelLatency absolutemillisecond2averageKernel Disk Command Latencyο
Average amount of time, in milliseconds, spent by VMkernel processing each SCSI command.
kernelReadLatency absolutemillisecond2averageKernel Disk Read Latencyο
Average amount of time, in milliseconds, spent by VMKernel processing each SCSI read command.
kernelWriteLatency absolutemillisecond2averageKernel Disk Write Latencyο
Average amount of time, in milliseconds, spent by VMKernel processing each SCSI write command.
maxTotalLatency absolutemillisecond3averageHighest Disk Latencyο
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 deltanumber3summationDisk Read Requestsο
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 deltanumber3summationDisk Write Requestsο
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 absolutemillisecond2averageQueue Command Latencyο
Average amount of time spent in the VMkernel queue, per SCSI command, during the collection interval.
queueReadLatency absolutemillisecond2averageQueue Read Latencyο
Average amount of time taken during the collection interval per SCSI read command in the VMKernel queue.
queueWriteLatency absolutemillisecond2averageQueue Write Latencyο
Average amount time taken during the collection interval per SCSI write command in the VMKernel queue.
read ratekiloBytesPerSecond2averageDisk Read Rateο
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 absolutemillisecond2averageDisk Command Latencyο
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 absolutemillisecond2averageDisk Read Latencyο
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 absolutemillisecond2averageDisk Write Latencyο
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 kiloBytesPerSecondrate1 (4)average (minimum) (maximum) (none)Disk Usage (Average)
Disk Usage (Minimum)
Disk Usage (Maximum)
Disk Usage (None)
ο
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 ratekiloBytesPerSecond2averageDisk Write Rateο
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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