Database Reference
In-Depth Information
VMware DRS does not take active queue depth or SIOC into account when
considering compute-based load-balancing operations at this stage.
Caution
Because SIOC works only on data stores hosting multiple VMs, any data store
where a single VM resides will have the full access to all of the queue depth.
Usually this would be less than the aggregate queue depth used across multiple
hosts to a given LUN. In some cases, this could cause a performance impact, such
as when all data stores share the same RAID groups or disk groups on the array.
We recommend you enable SIOC as a standard on all of your data stores when using
traditional block-based storage arrays, regardless of whether or not they are hosting
more than one VM. This will ensure if things change in the future you know that your
VMs will always receive their fair share of the storage IO performance resources
available. If you have an auto-tiering array, we would recommend using the traditional
default values of 30ms for the static latency threshold and not using the injector with
vSphere 5.5.
Tip
We recommend you enable SIOC as a standard on all of your data stores,
regardless of whether or not they are hosting more than one VM.
Note
The recommendations to use SIOC assume traditional block-based shared
storage architecture is being used. Some modern storage systems don't
suffer from the problems that caused a need to have SIOC in the first place,
and therefore there is no need to use SIOC on these systems. An example is
the Nutanix Virtual Computing Platform, where data access is localized per
host, although it provides a distributed shared storage environment. In this
case, disk shares on each host ensure fairness of IO performance. The
Nutanix platform doesn't suffer from the problems that SIOC addresses,
and therefore SIOC is not required.
Figure 6.31
shows the vSphere 5.5 Storage IO Control Settings dialog box. By setting
SIOC to Manual, you effectively disable the injector, which is the preferred setting
when using auto-tiering arrays, or storage platforms where the injector is likely to get
inaccurate data.
