Storage DRS FAQ

Storage DRS Cluster

 

What are functions get enabled when you enable storage DRS?

Space load balancing among datastores within datastore cluster

I/O load balancing among datastores within datastore cluster

Initial placement for virtual disks on space and I/O workload

When you disable storage DRS all the above functions gets disabled but you can specifically disabled I/O load balancing. When you disable Storage DRS unlike DRS all settings are preserved to the point where Storage DRS was disabled.

When an initial placement does happen?

  1. When VM is created
  2. When VM is cloned
  3. When VM is migrated to another datastore cluster
  4. When you add a disk to existing VM

On what basis Initial recommendations are made?

  1. Datastores user defined space utilization threshold
  2. I/O latency
  3. Anti-affinity rules

When is storage DRS invoked?

  1. It is invoked at the configured frequency i.e. every 8 hours (this is default)
  2. When space of one of the datastore in a datastore cluster exceeds user configurable space utilization threshold.

What happens when storage DRS is invoked?

When storage DRS is invoked it checks each datastores space utilization and I/O latency values against threshold. For I/O latency, storage DRS uses the 90th percentile I/O latency measured over the course of a day to compare against the threshold.

What are the reasons for recommendations?

  1. Balance datastore space use
  2. Balance datastore I/O load

When does storage DRS makes mandatory recommendations

The datastore is out of space

Anti-affinity or affinity rules are being violated

The datastore is entering maintenance mode and must be evacuated

However optional recommendations are made when datastore is about to run out of space or when adjustment should be made for space and I/O load balancing.

Does virtual machine states are considered when Storage DRS is invoked?

Storage DRS is focused on disk space. Therefore state of virtual machine does not matter. So Storage DRS considers moving virtual machine which are powered on or powered off for space balancing.

How many automation level are available for Storage DRS?

In storage DRS unlike DRS only two automation level are available.

No Automation (Manual): Same as DRS i.e. both initial placement and migration recommendation needs to be implemented manually.

Fully automated: Everything is automated without any manual intervention

What are requirements of datastore cluster?

  • Datastore cluster must contain similar datastore. It can have different sizes, disks and even different arrays and vendors. But following types of datastore cannot exist
    • NFS & VMFS cannot be mixed, you can make VMFS based datastore cluster or NFS based datastore cluster
    • Replicated datastores cannot be mixed with non-replicated datastores.
  • All hosts must be ESXi5.0 or above
  • Datastores shared across multiple datacenters cannot be included in datastore cluster
  • VMware recommends not mixing array which has hardware acceleration support with non-hardware acceleration support. Datastores in a datastore cluster must be homogenous to take advantage of hardware assisted features