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: https://pubs.vmware.com/vsphere-50/index.jsp?topic=%2Fcom.vmware.vsphere.storage.doc_50%2FGUID-061BE1F4-9EA9-49F4-A537-05EFAFC9BB0E.html

VMFS-5 Partitioning

Upgrading from VMFS-3 to VMFS-5

• 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>

Troubleshooting VMFS-5 Upgrade Issues

• 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:
   
  • Upgrade this host to ESXi 5.x.
  • vMotion all VMs accessing this datastore from the legacy ESX host to an ESXi 5.x host.
  • Storage vMotion, or Cold Migrate the virtual machines to a VMFS-3 filesystem.
  • Un-present the datastore from the legacy ESXi host. For more information see Removing a LUN containing a datastore from VMware ESXi/ESX 4.x (1029786).