Compressed volumes
When you create volumes, you can specify compression as a method to save capacity for the volume. With compressed volumes, data is compressed as it is written to disk, saving more space. To use the compression function, you must obtain a compression license.
Like thin-provisioned volumes, compressed volumes have virtual, real, and used capacities. Use the following guidelines before you work with compressed volumes.
- Real capacity is the extent space that is allocated from the pool. The real capacity is also set when the volume is created and like thin-provisioned volumes, can be expanded or shrunk down to the used capacity.
- Virtual capacity is available to hosts. The virtual capacity is set when the volume is created and can be expanded or shrunk afterward. The virtual capacity of a HyperSwap® volume cannot be changed. To expand or shrink the volume, you must convert the HyperSwap volume to a basic volume by removing a copy from the volume. The volume can then be resized and a new copy can be added again to convert the volume back into a HyperSwap volume.
- Used capacity is the amount of real capacity that is used to store customer data and metadata after compression.
- Capacity before compression is the amount of customer data that was written to the volume and then compressed. The capacity before compression does not include regions where zero data is written to unallocated space.
You can also monitor information on compression usage to determine the savings to your storage capacity when volumes are compressed. To monitor system-wide compression savings and capacity, select . You can compare the amount of capacity that is used before compression is applied to the capacity that is used for all compressed volumes. In addition, you can view the total percentage of capacity savings when compression is used on the system. You can also monitor compression savings across individual pools and volumes. For volumes, you can use these compression values to determine the volumes that achieved the highest compression savings.
If your system currently does not use compression, the system automatically analyzes your configuration to determine the potential storage savings if compression is used. The management GUI incorporates the Comprestimator utility that uses mathematical and statistical algorithms to create potential compression savings for the system. The analysis for potential savings can be used to determine whether purchasing a compression license for the system is necessary to reduce cost of extra storage devices. To estimate compression savings in the management GUI, select .
Benefits of Compression
Using compression reduces the amount of physical storage across your environment. You can reuse free disk space in the existing storage without archiving or deleting data.
Compressing data as it is written to the volume also reduces the environmental requirements per unit of storage. After compression is applied to stored data, the required power and cooling per unit of logical storage is reduced because more logical data is stored on the same amount of physical storage. Within a particular storage system, more data can be stored which reduces overall rack unit requirements.
Compression can be implemented without impacting the existing environment and can be used with other storage processes, such as mirrored volumes and Copy Services functions.
Compressed volumes provide an equivalent level of availability as regular volumes. Compression can be implemented into an existing environment without an impact to service and existing data can be compressed transparently while it is being accessed by users and applications.
When you use compression, monitor overall performance and CPU utilization to ensure that other system functions have adequate bandwidth. If compression is used excessively, overall bandwidth for the system might be impacted. To view performance statistics that are related to compression, select and then select Compression % on the CPU Utilization graph.
Common uses for compressed volumes
Compression can be used to consolidate storage in both block storage and file system environments. Compressing data reduces the amount of capacity that is needed for volumes and directories.
Compression can be used to minimize storage utilization of logged data. Many applications, such as lab test results, require constant recording of application or user status. Logs are typically represented as text files or binary files that contain a high repetition of the same data patterns. Database information is stored in table space files. It is common to observe high compression ratios in database files.