Tag Archive: Storage DRS

When a virtual machine is provisioned to the datastore cluster, Storage DRS algorithm runs to determine the best placement of the virtual machine. The interesting part of this process is the method Storage DRS determines the free space of a datastore or to be more precise the improvement made in vSphere 5.1 regarding free space calculation and the method of finding the optimal destination datastore.

vSphere 5.0 Storage DRS behavior
Storage DRS is designed to balance the utilization of the datastore cluster, it selects the datastore with the highest free space value to balance the space utilization of the datastores in the datastore cluster and avoids out-of-space situations.

During the deployment of a virtual machine, Storage DRS initiates a simulation to generate an initial placement operation. This process is an isolated process and retrieves the current datastore free space values. However, when a virtual machine is deployed, the space usage of the datastore is updated once the virtual machine deployment is completed and the virtual machine is ready to power-on. This means that the initial placement process is unaware of any ongoing initial placement recommendations and pending storage space allocations. Let’s use an example that explains this behavior.


More information about this article in frankdenneman.nl


vSphere 5.0 introduces many great new features, but everyone will probably agree with us that vSphere Storage DRS is most the exciting new feature. vSphere Storage DRS helps resolve some of the operational challenges associated with virtual machine provisioning, migration and cloning. Historically, monitoring datastore capacity and I/O load has proven to be very difficult. As a result, it is often neglected, leading to hot spots and over- or underutilized datastores. Storage I/O Control (SIOC) in vSphere 4.1 solved part of this problem by introducing a datastore-wide disk-scheduler that allows for allocation of I/O resources to virtual machines based on their respective shares during times of contention.

Storage DRS (SDRS) brings this to a whole new level by providing smart virtual machine placement and load balancing mechanisms based on space and I/O capacity. In other words, where SIOC reactively throttles hosts and virtual machines to ensure fairness, SDRS proactively makes recommendations to prevent imbalances from both a space utilization and latency perspective. More simply, SDRS does for storage what DRS does for compute resources.

There are five key features that SDRS offers:

  • Resource aggregation
  • Initial Placement
  • Load Balancing
  • Datastore Maintenance Mode
  • Affinity Rules

For those who want more details, Frank Denneman wrote an excellent series about Datastore Clusters which might interest you:

Part 1: Architecture and design of datastore clusters.
Part 2: Partially connected datastore clusters.
Part 3: Impact of load balancing on datastore cluster configuration.
Part 4: Storage DRS and Multi-extents datastores.
Part 5: Connecting multiple DRS clusters to a single Storage DRS datastore cluster.
Part 6: Aggregating datastores from multiple storage arrays into one Storage DRS datastore cluster.

Some other articles that might be of use:

Source: Yellow Bricks Blog


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