Everything you want to know about VMFS5

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If you want to know everything there is to know about VMFS5. please read this document.

There is more to VMFS than base disks, descriptor files and extends than you think.

VMFS-5 Overview

Why switch to VMFS-5?

  • VMFS-5 has improved scalability and performance.
  • VMFS-5 does not use SCSI-2 Reservations, but uses the ATS VAAI primitives.
  • VMFS-5 uses GPT (GUID Partition Table) rather than MBR, which allows for pass-through RDM files greater than 2TB.
  • Newly created VMFS-5 datastores use a single block size of 1MB.
  • VMFS-5 has support for very small files (<1KB) by storing them in the metadata rather than in the file blocks.
  • VMFS-5 uses sub-blocks of 8K rather than 64K, which reduces the space used by small files.
  • VMFS-5 uses SCSI_READ16 and SCSI_WRITE16 cmds for I/O (VMFS-3 used SCSI_READ10 and SCSI_WRITE10 cmds for I/O).

What are the limitations for VMFS-5?

  • VMFS-5 still limits the number of extents to 32 and the total datastore size to 64TB, but the individual extents are no longer limited to 2TB each. For example, a datastore can be created with a LUN size of 64TB, or a datastore can be created with up to 32 extents up to maximum size of 64TB.
  • Only pass-through RDMs (Raw Device Mapping) can be created with a size >2TB. Non-pass-through RDMs and virtual disk files are still limited to 512B ~ 2TB.
  • Passthrough RDMs are supported up to ~60TB in size.
  • Both upgraded and newly-created VMFS-5 volumes supported the larger Passthrough RDM size.

Non-passthrough RDMs are still limited to 2TB minus 512B.


Note:-
The actual maximum size of a LUN will depend on the capabilities of RAID controller/adapter driver that is used on the vSphere host.
For vSphere 5.0 storage configuration maximums pertaining to 2TB LUN support please review Configuration Maximums for VMware vSphere 5.0

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