Monitoring physical capacity

If you are using the command-line interface to determine physical capacity usage on your system, several parameter values are used from the lssystem command to calculate stored, available, and total capacities. Stored capacity is calculated with the values in the total_mdisk_capacity, total_free_space, total_reclaimable_capacity by using the following formula:

• Total stored capacity = total_mdisk_capacity - total_free_space - total_reclaimable_capacity

To calculate the available capacity, use the values in total_free_space and total_reclaimable_capacity in the following formula:

• Total available capacity = total_free_space + total_reclaimable_capacity

The value in the total_mdisk_capacity in the lssystem command indicates the total physical capacity on the system.

The system supports virtualizing capacity that is on external storage systems that are attached to the system. For external storage systems, administrators must configure out-of-space alerts that notify the system when physical capacity on the external storage system has reached a defined threshold. Without these thresholds defined on the external storage systems, external storage on these systems can become overprovisioned and risk running out of physical capacity that is used for host operations. Overprovisioned external storage occurs when the sum the provisioned capacity of all the volumes in a system or pool is greater than the total physical capacity of the system or pool that is allocated from the external storage system. The system detects potential overprovisioned external storage and presents a warning on the Dashboard page. If this warning displays, select Overprovisioned External Storage to display pools that contain storage that are nearing these overprovisioned scenarios. Depending on how external storage is configured in pools, different strategies and best practices can be used to ensure capacity is sufficient and reported accurately to the system.

Configuration Scenario 1: One pool contains storage from one external storage system

In this configuration, storage administrators have the same concern of running out of capacity as when data is written data directly to external storage systems. Storage administrators must set up out-of-space alerts on external storage and monitor usage to ensure that the I/O operations do not exceed the physical capacity. Consult documentation for your external storage system for specific guidelines on these thresholds. If an out-of-space condition occurs, then capacity must be freed by deleting data or volumes.

Configuration Scenario 2: Multiple pools contain a single tier of storage from multiple external storage system

In this configuration, multiple pools use the same type of storage, or tier, across several external storage systems. If capacity from different external storage systems is shared across multiple pools, then provisioning groups are created. Provisioning groups are objects that identify whether storage is shared across multiple pools. The MDisks by Pools page in the management GUI, displays all pools and their assigned MDisk. If you are not sure whether external storage systems are shared across several pools, right-click the pool and select View Resources to display the provisioning group that is associated with the pool. In this configuration, the system spreads extent allocations across all the external storage within the provisioning group to ensure space is consumed evenly across all the external storage systems. However, physical capacity usage on external storage systems within the provisioning groups can still become overprovisioned, so storage administrators need configure out-of-space alerts and monitor capacity to determine how space is being consumed. If low-space warning occurs on virtualized MDisks on external storage and physical capacity is available on other external storage system in the pool, you can remove some of these MDisks from the pool until the physical capacity usage is within reasonable limits. This process migrates data to other MDisks in the pool. Ensure that enough capacity is available on the other external storage systems in the pool so that they do not run out of space during this operation.

Configuration Scenario 3: Multiple pools contain a different tiers of storage from multiple external storage systems

In this configuration, different tiers of storage are present on the external storage systems within the pools. As with the previous configuration, provisioning groups are created to identify the storage that is shared with in the pools. However in this case the system attempts to allocate the entire physical capacity in the top tier rather than spreading extents across provisioning groups. Storage administrators need to monitor the physical capacity in these top tiers of storage to ensure space is sufficient for the workloads. If low-space warning occurs on virtualized MDisks on external storage and physical capacity is available on other external storage system in the pool, you can remove some of these MDisks from the pool until the physical capacity usage is within reasonable limits. This process migrates data to other MDisks in the pool. Ensure that enough capacity is available on the other external storage systems in the pool so that they do not run out of space during this operation.

Configuration Scenario 4: Data reduction pools

Systems that support data reduction pools, which use data reduction technologies, like compression, can configure these types of pools to minimize overallocation on the external storage system. Data reduction pools also support the ability to reclaim unused capacity from host unmap operations and volume deletions. In the management GUI, select Pools > MDisks by Pools to view all the pools configured on the system. Data reduction pools are shown with Data Reduction set to Yes. When using data reduction pools that virtualize external storage which can run out of space, always enable compression when you create volumes in these pools. The external storage system must be configured to present only physical capacity to the system, as the size of the written data written cannot be reduced any further.