What is VMware VMFS 5?

VMFS5: 
  • VMware proprietary file system that is virtualization aware and optimized for virtualization.
  • Supports concurrent access to shared storage.
  • Can be expanded dynamically.
  • Uses a 1 MB regular block size, for storing large virtual disk files.
  • Uses sub-block addressing, storing small files: the sub-block size is 8 KB.
    • If file size is less than 1 KB, file is stored in metadata space. No blocks/sub-blocks are used.
    • If file size is more than 1 KB but less than 8 KB, sub-block is used to store the file.
    • If file size is more than 8 KB, regular block is used.
  • Provides on-disk, block-level locking.
  • Maximum number of datastore per host: 1024
  • Maximum number of paths : 4096
  • Supported storage drives: 512n/512e
  • Supported Sparse format: vmfsSparse for VMDKs less than 2 TB and SEsparse for VMDKs equal to or greater than 2 TB

There are 2 methods used under on-disk, block level locking as below.

  • SCSI Reservations
  • ATS (Atomic Test and Set) – Default method if storage has VAAI plugin support.

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