6.0.1

DRS Support for Flash Read Cache
DRS supports virtual ash as a resource.
DRS manages virtual machines with Flash Read Cache reservations. Every time DRS runs, it displays the
available virtual ash capacity reported by the ESXi host. Each host supports one virtual ash resource. DRS
selects a host that has sucient available virtual ash capacity to start a virtual machine. DRS treats
powered-on virtual machines with a Flash Read Cache as soft aned to their current host and moves them
only for mandatory reasons or if necessary to correct host over-utilization.
vSphere High Availability Support for Flash Read Cache
Flash Read Cache is supported by High Availability (HA).
When vSphere HA restarts a virtual machine congured with Flash Read Cache, the virtual machine is
restarted on a host in the cluster where the Flash Read Cache, CPU, Memory and overhead reservations are
met. vSphere HA will not restart a virtual machine if unreserved ash is insucient to meet the virtual ash
reservation. You must manually recongure a virtual machine to reduce or drop the Flash Read Cache, if the
target host does not have sucient virtual ash resource available.
Configure Flash Read Cache for a Virtual Machine
You can congure 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.
Prerequisites
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Set up virtual ash resource.
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Verify that the virtual machine is compatible with ESXi 5.5 or later.
Procedure
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 .
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.
vSphere Storage
142 VMware, Inc.