Example Architectural Decision – Storage DRS Configuration for VMFS Datastores in a vCloud Environment

Problem Statement

In a production , self service vCloud Director environment, What is the most suitable Storage DRS configuration to improve storage utilization , performance, as well as reduce administrative effort for BAU staff?

Requirements

1. Make the most efficient use of the available storage capacity
2. Maintain consistent level of storage performance
3. Reduce the risk and overhead of capacity management
4. Reduce the risk of a unintentional or otherwise DoS event caused by self service

Assumptions

1. vSphere 5.0 or later
2. VMFS 5 Datastores which are Thick Provisioned
3. Deduplication is not in use
4. VAAI is supported by the array and enabled across the vSphere environment
5. All datastores in each respective Datastore clusters reside on the same RAID type with similar spindle types and count
6. All datastores are presented to all hosts within the cluster
7. Array level snapshots are not in use
8. IBM SVC Storage is being used
9. vCloud Director 5.1 or later
10. Storage I/O Control is enabled at set to 30ms

Constraints

1. IBM SVC storage does not currently support VASA (VMware API for Storage Awareness)

Motivation

1. Ensure production storage performance is not negatively impacted
2. Minimize the vSphere administrators workload where possible

Architectural Decision

Set the DRS automation setting to “Fully Automated”

  • Set “Utilized Space” threshold to 80%
  • Set “I/O latency” to 15ms
  • I/O Metric Inclusion – Enabled

Advanced Options

  • No recommendations until utilization difference between source and destination is: 10%
  • Evaluate I/O load every 8 Hours
  • I/O Imbalance threshold  4

Justification

1. Setting Storage DRS to “Fully Automated”  ensures that the administrator does not need to be concerned with initial placement of virtual machines as this will be dynamically and intelligently determined and executed

2. “XCOPY” is fully supported for Block based storage, as such, any Storage vMotion activity is offloaded to the array therefore removing the I/O overhead on the compute and storage fabric.

3. Where a significant I/O imbalance is detected by SDRS, the vSphere administrator is not required to take any action, Storage DRS can identify and remediate issues which fall outside parameters (which are determined by the VMware Architect) automatically. This improves the efficiency of the environment, and reduces the involvement of BAU.

4. SDRS provides valuable “initial placement” for new virtual machines which will help avoid a situation where datastores are unevenly balanced from a capacity perspective in the first place, therefore reducing the chance of virtual machines requiring migration.

5. Setting the “No recommendations until utilization difference between source and destination is” to 20% ensures that SDRS does not move virtual machines around where significant benefit is not realized  This prevents unnecessary Storage vMotion activity on the disk system, although this is offloaded from the host to the array, the I/O still may impact production performance for workloads on the same disk system.

6. Setting the “I/O Imbalance threshold (5 Aggressive / Conservative 1 ) to “4” (2nd most aggressive)  ensures that I/O imbalance should be addressed before significant imbalance is experienced by the end users. This level of “ aggressiveness” is acceptable as the Storage vMotion can be offloaded (via VAAI “XCOPY” primitive  and has almost zero impact on the host.  Setting this to “5” may result in minor I/O imbalances being corrected, at the cost of a Storage vMotion and as a result the impact of the more frequent Storage vMotion activity may negate the benefit of the I/O balancing.

7. Storage DRS will address I/O imbalance across the datastore cluster if the latency meets or exceeds the set value of 15ms (the default) and in the event of latency increasing during peak times to >=30ms , Storage I/O Control will ensure fair acess to the storage.

Alternatives

1. Use “No Automation (Manual Mode)”
2. Not use Storage DRS

Implications

1. When selecting datastores for the datastore cluster, having VASA enabled allows the “System Capability” column to be populated in the “New Datastore Cluster” wizard to ensure suitable datastores of similar performance, RAID type and features are grouped together. VASA is currently NOT supported by SVC, as such the datastore naming convension needs to accurately reflect the capabilities of the LUN/s to ensure suitable datastores are grouped together.

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Example Architectural Decision – Storage DRS Configuration for NFS Datastores

Problem Statement

In a vSphere environment, a NAS array is presenting Thin Provisioned NFS mounts (Datastores) to the vSphere environment. The storage has deduplication enabled across the datastores being used for the SDRS cluster. What is the most suitable configuration for SDRS to ensure the underlying storage efficiencies are not compromised while maintaining an even distribution of utilized capacity and I/O across all datastores?

Assumptions

1. vSphere 5.0 or later
2. NFS Based storage
3. NFS Mounts (Datastores) are Thin Provisioned
4. Deduplication is enabled on the array
5. VAAI is supported by the array and enabled across the vSphere environment
6. All datastores in a Datastore cluster are of the same RAID Type / Offer Similar performance due to having a similar spindle count
7. All datastores are presented to all hosts within the cluster

Motivation

1. Ensure storage efficiencies are not negatively impacted
2. Minimize the vSphere administrators workload where possible

Architectural Decision

Set the DRS automation setting to “No Automation (Manual Mode)”

  • Set “Utilized Space” threshold to 80%
  • Set “I/O latency” to 15ms
  • I/O Metric Inclution – Enabled

Advanced Options

  • No recommendations until utilization difference between source and destination is: 10%
  • Evaluate I/O load every 8 Hours
  • I/O Imbalance threshold  3

Justification

1. Setting Storage DRS to “No Automation (Manual Mode)” ensures that the administrator can confirm the recommendation will not Negatively impact the efficiency of Deduplication or  the thin provisioned NFS mounts
2. When creating a new Virtual Machine, in the “Ready to complete” window, Tick the “Show all storage recommendations” check box to review Storage DRS recommendations and override the recommendations where required
3. Where a VM is deduplicated on the source datastore, and it is moved to the destination datastore, this write activity is considered new data which will scanned by the post deduplication process which will use valuable CPU cycles on the array
4. “XCOPY” is not supported for NFS, as such, any Storage vMotion activity can only be offloaded to the array using the “Full File Clone” when a virtual machine is powered off.
5. Array level snapshots cannot be migrated with the VM using Storage DRS. If Virtual machines were automatically moved then the array level snapshot relasionship with the VM is broken and it cannot be leveraged
6. NFS datastores can be set to autogrow  by a predefined size in the event they reach a predefined utilization threashold
7. Where a significant I/O imbalance is detected by SDRS, the vSphere administrator can consider the impact of the Storage vMotion and where suitable apply the SDRS recommendation
8. SDRS still provides valuable “initial placement” for new virtual machines which will help avoid a situation where datastores are unevenly balanced from a capacity perspective
9. Storage DRS will still analysis I/O and where an imbalance is identified the vSphere administrator can choose to apply the SDRS recommendation to address the I/O imbalance

Implications

1. When selecting datastores for the datastore cluster, having VASA enabled allows the “System Capability” column to be populated in the “New Datastore Cluster” wizard to ensure suitable datastores of similar performance, RAID type and features are grouped together
2. A vSphere administrator will need to review SDRS recommendations

Alternatives

1. Use “Fully Automated”