I recently noticed VMware KB that talks about vSphere 5.x hosts may fail to mount an ATS-Only VMFS Datastore on some storage arrays.

VMware KB 2006858 – “ESXi 5.x hosts fail to mount VMFS5 volumes that are formatted with ATS-only capabilities” warns of this problem and lists some storage arrays where the problem is known to occur. It should be noted that the list of arrays that could see this problem is not exhaustive and other arrays could also be impacted.

ATS or Atomic Test and Set is the locking mechanism used when VAAI (vSphere API for Array Integration) capability is enabled. This allows your VMware environment to support many more VM’s per datastore than is possible when using standard SCSI reservations. Given the impact that this may have on affected environments it would pay to review the KB and also check with your storage vendor that your array fully supports VAAI. The alternative or suggested workaround is to disable VAAI across your clusters, which may impact performance and scalability.

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This post first appeared on the Long White Virtual Clouds blog at longwhiteclouds.com, by Michael Webster +. Copyright © 2012 – IT Solutions 2000 Ltd and Michael Webster +. All rights reserved. Not to be reproduced for commercial purposes without written permission.