6.0

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 those used for memory and CPU resource allocation, which are described
in the vSphere Resource Management publication. These shares represent the relative importance of a virtual
machine with regard to the distribution of storage I/O resources. Under resource contention, virtual
machines with higher share values have greater access to the storage array, which typically results in higher
throughput and lower latency.
When you allocate storage I/O resources, you can limit the IOPS that are allowed for a virtual machine. By
default, these are unlimited. If a virtual machine has more than one virtual disk, you must set the limit on all
of its virtual disks. Otherwise, the limit will not be enforced for the virtual machine. In this case, the limit on
the virtual machine is the aggregation of the limits for all virtual disks.
The benefits and drawbacks of setting resource limits are described in the vSphere Resource Management
publication. 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 backup application with 64KB IOs to 10MB 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 settings of all virtual machines that are accessing the datastore, regardless of the
cluster in which they are running.
Prerequisites
Launch the vSphere Client and log in to a vCenter Server system.
Procedure
1 Select the datastore in the vSphere Client inventory.
2 Click the Virtual Machines tab.
The tab displays each virtual machine running on the datastore and the associated shares value, IOPS
limit, 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
Prerequisites
Launch the vSphere Client and log in to a vCenter Server system.
vSphere Administration with the vSphere Client
350 VMware, Inc.