6.5.1

Storage I/O Control Resource Shares and Limits
You allocate the number of storage I/O shares and upper limit of I/O operations per second (IOPS) allowed
for each virtual machine. When storage I/O congestion is detected for a datastore, the I/O workloads of the
virtual machines accessing that datastore are adjusted according to the proportion of virtual machine shares
each virtual machine has.
Storage I/O shares are similar to shares used for memory and CPU resource allocation, which are described
in “Resource Allocation Shares,” on page 11. These shares represent the relative importance of a virtual
machine regarding the distribution of storage I/O resources. Under resource contention, virtual machines
with higher share values have greater access to the storage array. When you allocate storage I/O resources,
you can limit the IOPS allowed for a virtual machine. By default, IOPS are unlimited.
The benets and drawbacks of seing resource limits are described in “Resource Allocation Limit,” on
page 12. If the limit you want to set for a virtual machine is in terms of MB per second instead of IOPS, you
can convert MB per second into IOPS based on the typical I/O size for that virtual machine. For example, to
restrict a back up application with 64 KB IOs to 10 MB per second, set a limit of 160 IOPS.
View Storage I/O Control Shares and Limits
You can view the shares and limits for all virtual machines running on a datastore. Viewing this information
allows you to compare the seings of all virtual machines that are accessing the datastore, regardless of the
cluster in which they are running.
Procedure
1 Browse to the datastore in the vSphere Web Client navigator.
2 Click the VMs tab.
The tab displays each virtual machine running on the datastore and the associated shares value, and
percentage of datastore shares.
Monitor Storage I/O Control Shares
Use the datastore Performance tab to monitor how Storage I/O Control handles the I/O workloads of the
virtual machines accessing a datastore based on their shares.
Datastore performance charts allow you to monitor the following information:
n
Average latency and aggregated IOPS on the datastore
n
Latency among hosts
n
Queue depth among hosts
n
Read/write IOPS among hosts
n
Read/write latency among virtual machine disks
n
Read/write IOPS among virtual machine disks
Procedure
1 Browse to the datastore in the vSphere Web Client navigator.
2 Under the Monitor tab, click the Performance tab.
3 From the View drop-down menu, select Performance.
For more information, see the vSphere Monitoring and Performance documentation.
Chapter 8 Managing Storage I/O Resources
VMware, Inc. 51