Monitoring capacity savings

You can use the management GUI to determine the capacity savings that are created by thin-provisioning, compression, and deduplication.

The system supports several methods to save capacity. These methods can be used separately, but when used together they can provide greater capacity savings and efficiencies for the system. The system supports thin-provisioning, compression, and deduplication. With thin-provisioned volumes, the amount of capacity that can be provisioned to hosts is not limited by the usable capacity because the system eliminates the unused allocated capacity. A thin-provisioned volume presents a different capacity to mapped hosts than the capacity that the volume consumes in the storage pool. With thin provisioning, storage administrators can configure thin-provisioned volumes that can grow into the usable capacity they need based on the storage needs of the host. This flexibility saves on the costs to manage the storage capacity for host applications. Apart from standard-provisioned volumes, all volume types provide capacity savings and benefits from thin-provisioning. It can be used with compression and deduplication, or it can be used by itself. Thin-provisioning is supported in both standard pools and data reduction pools. However, data reduction pools support reclaiming capacity when it is no longer needed by hosts and then can redistribute it automatically for other uses.

Unlike thin-provisioning, which removes unused capacity, compression and deduplication increase the usable capacity by reducing the size of the data itself. The system supports several types of compression technologies that can be used on the system at the same time. Software-based compression is implemented when you create volumes, where compression can be enabled on the volume. With compressed volumes, data is compressed in the software then it is written to disk, saving more capacity. When data is read to hosts, the software decompresses the data. Compression is available through data reduction support as part of the system. If you want volumes to use compression as part of data reduction support, compressed volumes must belong to data reduction pools. Compressed volumes can also be created in standard pools, but data reduction pools support more capacity savings functions, such as automatic redistribution of reclaimed storage. The system also supports hardware-based compression technologies, such as self-compressing drives. This type of compression happens automatically within the hardware itself as data is written to the drive, and decompressed on the hardware as it is read to hosts. Depending on what technology handles the compression operations, a single capacity savings percentage for systems that use multiple compression technologies cannot be determined. Select Compression Details to view savings details for each of the compression technologies that are currently used on the system. If compressed volumes are configured in standard pools, you cannot create compressed volumes in data reduction pools within the same I/O group. Potential compression savings can be calculated for existing volumes in the management GUI through a built-in compression estimation tool. This tool can be used to determine the capacity savings that are possible for existing data on the system by using compression.

The system also supports deduplication. Deduplication can be configured with volumes that use different capacity saving methods, such as thin-provisioning. When you create a volume, you can specify to include deduplication with other supported capacity savings methods. Deduplicated volumes must be created in data reduction pools. If you have existing volumes in standard pools, you can migrate them to data reduction pools to add deduplication to increase capacity savings for the volume.

In addition to capacity savings from these methods, data reduction pools add another benefit by reclaiming capacity and redistributing it to other uses. Reclaimable capacity is calculated as part of the usable capacity on the system. The amount of reclaimable capacity varies based on the number of write operations and how much reclaimable capacity currently exists on the system. The reclaimable capacity represents usable capacity that will eventually become available for overwriting with new data when it is "reclaimed" and made available to the system. This reclaimable capacity is calculated and displayed with the usable capacity of the system. Since reclaimable capacity is not used by production data and is eventually reclaimed for use, the amount of reclaimable capacity is subtracted from stored capacity and added to available capacity in the Capacity tile on the Dashboard in the management GUI. This calculation gives a more accurate view of capacity usage on the system. You can also use the lssystem command to display the amount of total reclaimable capacity that currently exists on the system. In systems that contain self-compressing drives, the actual usable capacity that reclaimable capacity consumes cannot be calculated unless it is already compressed by the data reduction pool. When the data is compressed on the drive, it is not possible to determine how much usable capacity that becomes available when the reclamation process completes. Each of these capacity savings methods requires capacity monitoring to ensure efficient capacity provisioning on the system. Capacity savings result from using these methods and establishing best practices for capacity management in your organization and actual savings is contingent on these practices. However, compression and deduplication might provide data reduction two times greater than without these methods and thin-provisioning might provide two times the data reduction. When these data reduction methods are used together, overall capacity savings are combined.