How Storage Pools are Selected for Provisioning

Table of Contents

Overview

Learn how ViPR Controller automatically selects block and file physical storage pools for provisioning.

ViPR Controller runs filters against a set of storage pools that cover the physical storage systems associated with the virtual pools in the virtual arrays. If the storage pool meets all the filter criteria, it becomes a candidate for provisioning.

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Understanding pool utilization and subscription

ViPR Controller uses pool utilization and subscription when evaluating storage pools for provisioning.

The storage pool's capacity and subscription parameters are evaluated for pool utilization. Pool utilization is a calculation of the space that is currently being used compared to what is available as a percentage value. If the storage pool is below the utilization threshold, it is considered a match for provisioning.

Thick pool allocations are straight percentage values from 0 to 100%. Thin pools are allocated on-demand, and you can create volumes in excess of the pool size. A subscription percentage can be over 100%, implying that the aggregate size of the volumes provisioned pool is over the capacity. This over-subscription is limited to a certain percentage of the pool.

In the ViPR Controller user interface, you set the pool utilization and thin pool subscription on the Configuration Properties panel, shown below. To access this panel, select the Settings icon and then Configuration > Controller.

If you use the default Pool Utilization of 75% and the default Thin Pool Subscription of 300% on the Configuration Properties panel, the following occurs:
  • Thick and thin storage pools: If the space used is 75% or more of the available capacity, the physical storage pool is not a match for provisioning. If the thin storage pool is utilized more than the utilization limit, it is not a match for provisioning.
  • Thin storage pool: If the space subscribed is more than 300%, the physical thin storage pool is not a match for provisioning.

ViPR Controller Configuration Properties panel

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Selection process for block storage

ViPR Controller runs filters at volume creation and volume provisioning time. If the storage pool meets all the filter criteria, it becomes a candidate for block volume placement.

Filtering process

The following table explains the filters involved in the selection process.

Candidate storage pools

After the filters are run, a listing of candidate storage pools is created for volume placement. They are ordered according to these rules:

  • Least busy arrays and highest capacity pools
  • Ascending order of its storage system's average port usage metrics (first order)
  • Descending order by free capacity (second order)
  • Ascending order by ratio of pool's subscribed capacity to total capacity (suborder).

ViPR Controller uses this ordered list of storage pools to place the volumes. If the number of volumes is more than one, the volumes may be spread across the storage pools, depending on the sizes and the available storage pool capacity.

As the ViPR Controller places the volumes, it marks the volume capacity as reserved against the storage pool. This ensures that other provisions that happen subsequent to or during a volume creation are correctly distributed based on capacity. After the volume is created, or if there is an error in creating the volume, the reserved space is removed from the storage pool and the actual allocated space takes its place.

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Selection process for file storage

ViPR Controller runs filters at file creation. If the storage pool meets all the filter criteria, it becomes a candidate for file placement.

The following explains the selection process for file storage.

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