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Frequently Asked Questions on VMware vSphere 5.x for VMFS-5 (2003813)

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This article provides information on the new VMFS-5 filesystem in vSphere 5.x, as well as details regarding troubleshooting the upgrade between VMFS-3 and VMFS-5.


VMFS-5 Overview

Why switch to VMFS-5?

  • Improved scalability and performance.
  • Does not use SCSI-2 Reservations, but uses the ATS VAAI primitives.
  • Uses GPT (GUID Partition Table) rather than MBR, allowing for pass-through RDM files greater than 2TB.
  • VMFS5 in ESXi 5.5 now supports upto 62 TB VMDK and non-passthrough RDM. For more information, see Support for virtual machine disks larger than 2 TB in vSphere 5.5 (2058287).
  • Newly created VMFS-5 datastores use a single block size of 1MB.
  • Supports very small files (<1KB) by storing them in the metadata rather than in the file blocks.
  • Uses sub-blocks of 8K rather than 64K, which reduces the space used by small files.
  • 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 limits the number of extents to 32 and the total datastore size to 64TB, but the individual extents are not limited to 2TB each. For example, you can create a datastore with a LUN size of 64TB, or one 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 2TB -512B in 5.0 and 5.1. In ESXi 5.5, support for non-passthrough RDMs has been increased to 62TB.
  • Passthrough RDMs are supported up to 64TB in size.
  • Both upgraded and newly-created VMFS-5 volumes supported the larger Passthrough RDM size.
  • Verify that the volume to be upgraded has at least 2MB of free blocks available and 1 free file descriptor.  For more information see:

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.x storage configuration maximums pertaining to 2TB LUN support please review:
  • Configuration Maximums for VMware vSphere 5.0, 5.1, 5.5

VMFS-5 Partitioning

How to check my VMFS-5 partition information?

To allow files greater than 2TB, the partition table type has been changed from MBR to GPT. To view GPT partitioning, use the partedUtil command. For more information on this command for VMFS-5, see Using the partedUtil command line utility on ESXi/ESX (1036609).
My upgraded VMFS-5 partition information indicates MBR not GPT. Why?

Only extending the LUN/datastore beyond the 2TB limit automatically changes the partition type from MBR to GPT. If your LUN/datastore has not gone beyond this size, then the partition table stays at MBR.

Upgrading from VMFS-3 to VMFS-5

Can I upgrade while my virtual machines are running?

Yes. Upgrading from VMFS-3 to VMFS-5 can be done on-the-fly (virtual machines do not need to be powered-off, suspended, or migrated).

Do I have to use the command-line to upgrade to VMFS-5?

The upgrade to from VMFS-3 to VMFS-5 can be done either via the ESXi 5.x command-line or via vSphere Client.

: Ensure that all ESX hosts accessing the LUN are already on ESXi 5.x.
  • To upgrade to VMFS-5 using the vSphere Client, Under Configuration > Storage, highlight the desired VMFS-3 datastore, and click on Upgrade to VMFS-5...
  • To upgrade to VMFS-5 using the ESXi host command-line, use the command:

    # vmkfstools -T /vmfs/volumes/<VMFS3datastore>
My upgraded VMFS-5 does not have a 1MB block size. Why?

Upgraded VMFS-5 partitions will retain the partition characteristics of the original VMFS-3 datastore, including file block-size, sub-block size of 64K, etc. To take full advantage of all the benefits of VMFS-5, migrate the virtual machines to another datastore(s), delete the existing datastore, and re-create it using VMFS-5.

Note: Increasing the size of an upgraded VMFS datastore beyond 2TB changes the partition type from MBR to GPT. However, all other features/characteristics continue to remain same.

Troubleshooting VMFS-5 Upgrade Issues

The upgrade to VMFS-5 fails with these errors:
  • There are hosts accessing this datastore which don't support VMFS-5

    To resolve this issue, ensure all ESXi hosts accessing the datastore are already running ESXi 5.x.

  • An error occurred during host configuration. Operation failed, diagnostics report: Unable to Upgrade Filesystem: File system on device /vmfs/devices/disks/<device> cannot be online upgraded now because it is being used by some legacy host.

    To resolve this issue, check if any non-ESXi 5.x hosts (either standalone, or connected to another vCenter Server) is accessing this datastore, and has virtual machines running. If so, then run one of the:

Note: After the datastore is upgraded to VMFS-5, it is no longer visible on legacy ESXi hosts.

For more information, see the white paper VMware vSphere VMFS-5 Upgrade Considerations.


vmfs5 vmfs-block-size

See Also

Update History

01/03/2013 - Added link to the white paper VMware vSphere VMFS-5 Upgrade Considerations 11/01/2013 - Added vSphere 5.5 changes

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