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The PowerMax enables compression and deduplication using a feature that is called data reduction. Data reduction is enabled at the storage group level and uses both a hardware and software implementation. This data reduction is a combination of compression and deduplication. These two capabilities cannot be separated as they work together to achieve the required savings. However, each capability is explained separately below.
On the PowerMax, inline compression is available. Compression on the PowerMax is hardware-based, with the ability to use software in case a failure occurs. Individual devices cannot be compressed, rather compression is enabled at the storage group level for all devices within the group. Data is compressed as it is written to disk when the device is in a storage group with compression enabled. If compression is enabled on a storage group that already has data, a background process compresses that data. If compression is disabled on a storage group, new written data is not compressed but existing data is not immediately decompressed. Only when data is written again is it decompressed.
Note: Preallocated persistent devices cannot be compressed.
Note: Data reduction is not applicable on data that is stored on Storage Class Memory (SCM).
Deduplication works together with inline compression to further improve efficiency in the use of storage space. It reduces the number of copies of identical tracks that are stored on back-end devices. Depending on the nature of the data, deduplication can provide additional data reduction over and above the reduction that compression provides. Because deduplication works with compression on the PowerMax, one feature cannot be enabled without the other. When the PowerMax detects a duplicated track in a storage group, deduplication replaces it with a pointer to the track that already resides on back-end storage.
PowerMax deduplication with VMware is extremely effective at saving space when copies of virtual machines are made. Users can expect near one hundred percent deduplication.
Compression and deduplication on the PowerMax, as previously mentioned, is known as Data Reduction. It is complementary to thin provisioning. Not only can you oversubscribe storage initially, but as the data on the back-end can be compressed and deduped. By reducing the data footprint, it increases the effective capacity of the array.
The following example in Figure 87 shows where 1.3 PB of storage is presented to hosts in the form of thin devices. The physical storage behind the thin devices is only 1.0 PB. Adding data reduction reduces the required physical space by half, providing a 2:1 ratio. The array requires half as many drives to support the same front-end capacity.
Despite the space savings, if or when data is decompressed, additional space is required. It is considered when new arrays are sized.