Monitoring usable capacity
The system supports several ways to monitor usable capacity to ensure that storage is sufficient for host workloads.
Monitoring system-level capacity
The Capacity section on the Dashboard provides an overall view of system capacity. This section displays usable capacity, provisioned capacity, and capacity savings.
Usable capacity indicates the total capacity in all storage on the system. Usable capacity includes all the storage the system can be virtualized and assigned to pools. Usable capacity is displayed in a bar graph and is divided into three categories: Stored Capacity, Available Capacity, and Total. If the system supports self-compressing drives, certain system configurations make determining accurate usable capacity on the system difficult. For example, if the system contains self-compressed drives and data reduction pools without compression enabled, the system cannot determine the accurate amount of usable capacity that is used on the system. In this case, overprovisioning and losing access to write operations is possible. If this condition is detected by the system, the Usable Capacity section of the Dashboard page displays a message instead of capacity information. To recover from this condition, you need to ensure that all thin-provisioned volumes and thin-provisioned volumes that are deduplicated are migrated to volumes with compression enabled in the data reduction pools. Alternatively, you can migrate the volumes to standard-provisioned volumes and use the drive compression to save capacity.
- Total stored capacity = total_mdisk_capacity - total_free_space - total_reclaimable_capacity
- Total available capacity = total_free_space + total_reclaimable_capacity
Monitoring external storage systems, pool, and MDisk level capacity
- 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 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 usable capacity. Consult documentation for your external storage system for specific guidelines on these thresholds. If an out-of-space condition occurs, then usable capacity must be freed by deleting data or volumes.
- Configuration Scenario 2: Multiple pools contain a single tier of storage from multiple external storage systems
- 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 MDisks. 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 that space is used evenly across all the external storage systems. However, usable capacity on external storage systems within the provisioning groups can still become overprovisioned, so storage administrators need to configure out-of-space alerts and monitor usable capacity to determine how capacity is being used on the system. If low-space warning occurs on virtualized MDisks on external storage and usable capacity is available on other external storage system in the pool, you can remove some of these MDisks from the pool until the usable capacity is within reasonable limits. This process migrates data to other MDisks in the pool. Ensure that enough usable 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 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 external storage that is shared within the pools. However, in this case the system attempts to allocate the entire usable capacity in the top tier rather than spreading extents across provisioning groups. Storage administrators need to monitor the usable capacity in these top tiers of storage to ensure that space is sufficient for the workloads. If low-space warnings occur on virtualized MDisks on external storage and usable capacity is available on other external storage system in the pool, you can remove some of these MDisks from the pool until the usable capacity is within reasonable limits. This process moves data to other MDisks in the pool. Ensure that enough usable 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 to view all the pools configured on the system. Data reduction pools are shown with Data Reduction set to Yes. When you use data reduction pools that virtualize external storage that 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 usable capacity to the system, as the size of the written data cannot be reduced any further.
| Condition | Event ID | Error code | Percentage of usable capacity used |
|---|---|---|---|
| Compressed array is running low on usable capacity | 020009 | 1246 | 90% used |
| Critical level of compressed array is running low on usable capacity. | 020010 | 1246 | 96% |
| 1% usable capacity that is left for compressed array. | 020011 | 1242 | 99% |
| Compressed array out of usable capacity. | 020012 | 1241 | 100% |
If your system configuration dedicates specific storage systems to individual pools, analyzing the usable capacity for the pool can determine whether more usable capacity is needed. On the Pools page, check each MDisk in the pool for capacity and use the value for Storage System - LUN to determine the external storage system that provides the MDisk with space.