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RESXTOP Counters for Storage June 20, 2012

Posted by vbry21 in RESXTOP.
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Here is the final RESXTOP post, this one is about Storage.

Disk throughput can be monitored using RESXTOP.

The disk adapter screen hit the d key in RESXTOP.

READs/s – Number of disk reads per second

WRITES/s – Number of disk writes per second

The sum of reads/second and writes/second equals I/O operations/second (IOPS). IOPS is a common benchmark for storage subsystems and can be measured with tools like Iometer.

Disk throughput can also be monitored using the following metrics instead.

MBREAD/s – Number of megabytes read per second

MBWRTN/s – Number of megabytes written per second

As well as monitoring disk throughput, the disk adapter screen (type d in the window) lets us monitor disk latency as well, for myself, this is the counter I’m most interested in, purely because disk throughput does not necessarily mean we have an issue.

The following counters are of interest

ADAPTR – The name of the host bus adapter (vmhba#), which includes SCSI, iSCSI, RAID and Fibre Channel adapters.

DAVG/cmd – The average amount of time it takes a device (which includes the HBA, the storage array, and everything in between) to service a single I/O request (read or write).If the value < 10, the system is healthy. If the value is 11–20 (inclusive), be aware of the situation by monitoring the value more frequently. If the value is > 20, this most likely indicates a problem.

KAVG/cmd – The average amount of time it takes the VMkernel to service a disk operation. This number represents time spent by the CPU to manage I/O. Because processors are much faster than disks, this value should be close to zero. A value or 1 or 2 is considered high for this metric.

GAVG/cmd – The total latency seen from the virtual machine when performing an I/O request. GAVG is the sum of DAVG plus KAVG

 

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