VMware 6.0 vFlash Read Cache setup

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VMware vFlash Read Cache allows to leverage host local SSDs enabling a caching layer for the VMs. No other software or extra VIBs need to be installed on the host since all necessary modules are built-in the ESXi 6.0.

Using host local SSDs brings the benefit of offloading the I/O from the storage to the local SSD improving the performance. The read I/O instead of going directly to the storage, is acknowledged by the vFRC. Currently this feature support write-trough mode only making the system basically a read cache system.

SSDs used for vFRC are formatted using a special file system called VFFS (Virtual Flash File System) and they are aggregated into a pool forming a virtual flash resource available to the VMs as read cache.

 

Requirements and limits

  • VMware Enterprise Plus license
  • Supported storage device interface: SATA, SAS and PCI Express.
  • 1 virtual flash resource per host
  • 400 GB maximum cache for each virtual disk
  • 2 TB Cumulative cache configured per host (for all virtual disks)
  • 16TB virtual disk size
  • 4 TB virtual host swap cache size
  • 8 flash devices per virtual flash resource

 

Setup vFlash Read Cache

From vSphere Web Client, select the host you want to enable the vFlash Read Cache and go to Manage > Settings and select Virtual Flash Resource Management item.

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On the right side click on Add Capacity button.

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Select the flash device to use then click OK. The selected SSD is formatted using the VSSF file system erasing all existing data on the disk.

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After few seconds, the new resource is displayed showing the Capacity and the File System type.

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Repeat same procedure for all hosts where the vFlash Read Cache should be enabled.

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Select each host and go to the Summary tab to check the Virtual Flash Resource availability.

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Enable vFlash on a VM

To enable vFlash on virtual machine, right click the VM and select Edit Settings.

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Expand the Hard Disk to accelerate and in the Virtual flash read cache field enter the amount of GB to use as a cache. Click OK to apply changes.

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Click on Advanced link to access the advanced configuration to set the block size.

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Here you can specify the Reservation and also the value for Block Size useful to optimize some specific applications.

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Keep in mind that vFlash Read Cache feature is available only with the vSphere Enterprise Plus license.

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