6.0.1

Use Disk Shares to Prioritize Virtual Machines
You can change the disk resources for a virtual machine. If multiple virtual machines access the same VMFS
datastore and the same logical unit number (LUN), use disk shares to prioritize the disk accesses from the
virtual machines. Disk shares distinguish high-priority from low-priority virtual machines.
You can allocate the host disk's I/O bandwidth to the virtual hard disks of a virtual machine. Disk I/O is a
host-centric resource so you cannot pool it across a cluster.
Shares is a value that represents the relative metric for controlling disk bandwidth to all virtual machines.
The values are compared to the sum of all shares of all virtual machines on the server.
Disk shares are relevant only within a given host. The shares assigned to virtual machines on one host have
no effect on virtual machines on other hosts.
You can select an IOP limit, which sets an upper bound for storage resources that are allocated to a virtual
machine. IOPs are the number of I/O operations per second.
Procedure
1 Right-click a virtual machine in the inventory and select Edit Settings.
2 On the Virtual Hardware tab, expand Hard disk to view the disk options.
3 In the Shares drop-down menu, select a value for the shares to allocate to the virtual machine.
4 If you selected Custom, enter a number of shares in the text box.
5 In the Limit - IOPs box, enter the upper limit of storage resources to allocate to the virtual machine, or
select Unlimited.
6 Click OK.
Configure Flash Read Cache for a Virtual Machine
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.
Prerequisites
n
Set up virtual flash resource.
n
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 Settings.
Chapter 6 Configuring Virtual Machine Hardware
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