vSphere 5.1 Storage Enhancements – Part 9: Storage DRS

This post will look at Storage DRS enhancements in vSphere 5.1.

vCloud Directory Interoperability

In part 3 of this series on vSphere 5.1, I covered the storage enhancements to vCloud Director. One of the improvements in vSphere 5.1 for vCloud Director was Storage DRS interoperability. vCloud Director will use Storage DRS for the initial placement of vApps during Fast Provisioning vCloud Director will also use Storage DRS for the ongoing management of space utilization and I/O load balancing of the datastores in the Storage DRS datastore cluster. This is a great feature to have included with vCD, as it will offload many of the manual storage management tasks which an administrator has to carry out right now.

Datastore Correlation Detector

Datastore correlation refers to the fact that two distinct datastores could be using the same set of disk spindles at the back-end.

The ability to detect datastore correlation is already in Storage DRS but requires VASA to work. (VASA is short for vSphere Storage APIs for Storage Awareness). The purpose of the datastore correlation feature is to help the decision-making process in Storage DRS when deciding where to move a VM. For instance, there is little advantage moving a VM from one datastore to another if both datastores are backed by the same set of physical spindles on the array. This enhancement to the Datastore Correlation Detector now uses the Storage I/O Control I/O injector to determine if a source and destination datastore are correlated, i.e. using the same back-end spindles. It basically works by monitoring load on one datastore and monitoring the latency on another. If we see latency increases on both datastores when load placed on one datastore, we can assume the datastores are correlated. This decision is made after monitoring the behaviour over a period of time.

The Datastore Correlation Detector can also be used for Anti-Affinity rules, making sure that VMs & VMDKs are not only kept on separate datastores but are also kept on different spindles on the back-end.

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6 Replies to “vSphere 5.1 Storage Enhancements – Part 9: Storage DRS”

    1. Jonathan,
      Just noticed I hadn’t replied to this – sorry.
      I don’t believe there is any tagging done to the datastores – it is simply that they won’t be used in the algorithms of Storage DRS as possible destinations for Storage vMotion migrations.

  1. Hi Cormac,

    Couple of queries based on this KB related to SIOC/SDRS logging.


    1. It advises to increase the collection level to 3 from 1 to reduce the amount of logging and increased vCenter DB performance; but at the same time says that non-real time data would not be available if the collection level is increased.

    a. Is there an optimal way where we can keep historical performance data without impacting DB performance..?
    b. In general what’s the calculation in regards vCenter DB growth when SIOC/SDRS enabled..? How much will the DB grow (for ex: based on No. of VMs)..? Any other precautions to be taken etc..?
    Thanks for your time!

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