You can configure Flash Read Cache for a virtual machine compatible with ESXi 5.5 or later.

Enabling Flash Read Cache lets you specify block size and cache size reservation.

Block size is the minimum number of contiguous bytes that can be stored in the cache. This block size can be larger than the nominal disk block size of 512 bytes, between 4KB and 1024KB. If a guest operating system writes a single 512 byte disk block, the surrounding cache block size bytes will be cached. Do not confuse cache block size with disk block size.

Reservation is a reservation size for cache blocks. There is a minimum number of 256 cache blocks. If the cache block size is 1MB, then the minimum cache size is 256MB. If the cache block size is 4K, then the minimum cache size is 1MB.

For more information about sizing guidelines, search for the Performance of vSphere Flash Read Cache in VMware vSphere white paper on the VMware web site.


  • Set up virtual flash resource.
  • Verify that the virtual machine is compatible with ESXi 5.5 or later.


  1. To locate a virtual machine, select a data center, folder, cluster, resource pool, host, or vApp.
  2. Click the Related Objects tab and click Virtual Machines.
  3. Right-click the virtual machine and select Edit Settings.
  4. On the Virtual Hardware tab, expand Hard disk to view the disk options.
  5. To enable Flash Read Cache for the virtual machine, enter a value in the Virtual Flash Read Cache text box.
  6. Click Advanced to specify the following parameters.
    Option Description
    Reservation Select a cache size reservation.
    Block Size Select a block size.
  7. Click OK.