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Storage Implementation in vSphere® 5.0 by Mostafa Khalil

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Chapter 14. Distributed Locks

By default a logical unit number (LUN) is not designed to be accessed simultaneously by multiple hosts. VMware developed Virtual Machine File System (VMFS), their clustered file system, to allow ESXi hosts concurrent access to shared datastores. To prevent corruption resulting from more than one host writing to the same file or metadata area, an on-disk distributed locking mechanism is used. To put it simply, VMFS “tells” each host which areas in the metadata and disk it can update. It tracks this via on-disk lock records in the metadata. At the time each ESXi host was first installed and configured, it is assigned a unique ID referred to as Host UUID (Universally Unique Identifier). You can locate this ID on each ...

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