Tier definitions and volume placement optimization

Maximize storage efficiency by organizing the storage in your data center into tiers and implementing the recommendations that are generated to optimize the placement of volumes.

When you tier storage you can maximize the storage efficiency of your data center and gain insights into storage trends. The knowledge that you gain over time can help you plan investment in storage resources such as whether you need to invest in expensive tier-1 storage resources or whether less expensive storage resources, such as tier-2 or tier-3 storage resources, meet the storage needs of your data center.

Check the following sections to find out more about tiering your data center:
Tip: To define tiering criteria and threshold limits, click Configuration > Tiers.

Thresholds for tiering storage

Storage tiers comprise a set of pools that share hardware and performance characteristics. You set threshold levels for each tier to determine whether volumes are correctly tiered and to determine the optimum placement of volumes.

For each tier of storage, you can define the following criteria:
Threshold Type
The type of threshold that you want to use to place volumes on the right tier. You can choose one of the following threshold types to determine the placement of volumes on all of the tiers that you create:
  • I/O density (the number of I/O operations per second per GiB of storage)
  • I/O rate (the number of I/O read and write operations per second)
Threshold Value
The volumes with threshold values that are lower than the value that you specify are identified as candidates for re-tiering. Recommendations are generated to move the volumes to the next lowest tier.

Example: Down-tiering volumes

In this example, the threshold type that is selected to tier volumes is the I/O rate.

When data is collected, the volumes that do not meet the threshold values that you specify for each tier are identified and recommendations are generated to down-tier the volumes.

Example of down-tiering volumes

In this example, you create three storage tiers. You choose volume I/O rate as the threshold type, and you specify 5,000 as the threshold value for tier 1 and 1,000 as the threshold value for tier 2. You don't choose a threshold type or specify a threshold value for the lowest tier, tier 3. The threshold type of the lowest tier is automatically set to the threshold type of the next highest tier, which in this example is volume I/O rate, and the threshold value is automatically set to a value less than the threshold value of the next highest tier, which is <1,000 .

Each time data is collected, the I/O rate of the volume is compared with the I/O rate threshold for the tier. For example, the I/O rates of the volumes that are currently assigned to tier-1 pools are as follows:
  • 6,000 I/O operations per second
  • 3,000 I/O operations per second

Because the volume with 3,000 I/O operations per second is less than the minimum threshold limit for tier-1 pools, the volume is identified as a candidate for down-tiering. In this case, a recommendation is generated to move the volume with 3000 I/O operations per second to a pool on tier 2.

Information about defined tiers

When you define tiers, you can see the following information on the Tiers page:
  • The total capacity for each tier
  • The number of pools on the tier
  • The threshold type that was defined for the tiers
  • The range of values for the tier based on the down-tiering thresholds that you entered when you created the tier
For example, you created three tiers with the following values for down-tiering volumes:
  • 5,000 I/O operations per second for tier 1
  • 1,000 I/O operations per second for tier 2
The upper limit of the threshold value for the lowest tier, tier 3, is automatically set to a value less than the threshold value of the next highest tier.
When you save the tier definitions, you see the following values in the Range column on the Tiers page:
  • The range that is shown for tier 1 is >5000. When a scheduled data collection occurs, recommendations are generated to down-tier volumes with I/O rates less than 5,000 I/O operations per second.
  • The range that is shown for tier 2 is 1000 - 5000. When a scheduled data collection occurs, recommendations are generated to down-tier volumes with I/O rates less than 1,000 I/O operations per second.
  • The range that is shown for tier 3 is <1000. When a scheduled data collection occurs, no recommendations are generated. Volumes cannot be placed on a tier lower than the lowest tier.
Tip: To see a list of the pools that are not tiered, click the Untiered link in the doughnut chart. Select the pools that you want to tier, click Actions > Set Tier, and then select a tier level.