Troubleshooting poor storage controller performance

You can use the utility esxtop to help assess the bottleneck.


To use esxtop to help assess the bottleneck:

  1. Log into the ESX server console.
  2. Execute the command esxtop
  3. Press d to go to the disk statistics screen.
  4. Press f to go to the field selector.
  5. 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.
  6. 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.



About PiroNet

Didier Pironet is an independent blogger and freelancer with +15 years of IT industry experience. Didier is also a former VMware inc. employee where he specialised in Datacenter and Cloud Infrastructure products as well as Infrastructure, Operations and IT Business Management products. Didier is passionate about technologies and he is found to be a creative and a visionary thinker, expressing with passion and excitement, hopefully inspiring and enrolling people to innovation and change.
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