You can use the utility esxtop to help assess the bottleneck.
To use esxtop to help assess the bottleneck:
- Log into the ESX server console.
- Execute the command esxtop
- Press d to go to the disk statistics screen.
- Press f to go to the field selector.
- If the J does not have an asterisk (*) beside it, press j to add that field to the view. You can remove E from the view.
- Look for the DAVG/cmd field (device latency). This gives you an idea of how long the ESX host is waiting (in milliseconds) for SCSI commands submitted to the storage to come back with a response.
If the commands appear to have a considerable amount of latency (more than 50 ms) for the local vmhba, device contention is being encountered.
- Write performance is degraded on RAID controllers that have a discharged or absent battery because the write cache is disabled.
Check the battery to ensure that it’s present and/or charged. Your SCSI controller may not necessarily be faulty.
- Your RAID type may have some bearing on performance, particularly if it is not extremely poor, yet lower than your expected baseline.
The number of spindles/disks used per volume, along with the speed of the disks has an impact on performance.
- If a volume is degraded, such as having a failed drive in a RAID-5 disk set, read and write performance is severely hampered. You can check your RAID status in your array manager, or by observing the server’s indicator/warning lights, when and where applicable.
- As a troubleshooting measure, it may be worth breaking the disks into a RAID-less configuration, to eliminate this as being a possibility. This may require a reinstallation of VMware ESX.