Our GSS folks just released KB article 2049103 which details a VMFS Heartbeat and Lock corruption issue that manifests itself on DELL EqualLogic storage arrays when running PS Series firmware v6.0.6. As per the KB:
A VMFS datastore has a region designated for heartbeat types of operations to ensure that distributed access to the volume occurs safely. When files are being updated, the heartbeat region for those files is locked by the host until the update is complete.
In this scenario, the heartbeat region has become corrupt.
A full list of symptoms is documented in the KB article. The solution is to apply a new release of firmware recently released from DELL:
To prevent this issue from occurring, both VMware and Dell recommend upgrading the firmware to PS Series v6.0.6-H2 or later.
If you are running virtual machines on VMFS on EqualLogic storage, schedule some maintenance and get this new version of firmware installed asap.