Home > Storage > PowerMax and VMAX > Storage Admin > Dell PowerMax and VMware vSphere Configuration Guide > Thin device data reduction
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.
By default, when creating a storage group through Unisphere for PowerMax, the Data Reduction check box is enabled as in and Figure 88. Recall that if compression is enabled, deduplication is also enabled on PowerMax. PowerMax calls the two features “Data Reduction.” There is no separate check box for deduplication as enabling and disabling compression includes deduplication. When using a parent storage group, it is possible to set data reduction differently for each child storage group.
If using Solutions Enabler to create a storage group, data reduction is enabled by default provided the SRP is supplied on the command line. For instance, in Figure 89 storage group data_reduction_sg is created in SRP srp_1. Therefore, compression is enabled.
If the SRP is left out of command, the storage group no_data_reduction_sg is created without compression as in Figure 90.
If the user attempts to create the storage group with the -compression flag while still not providing an SRP, Solutions Enabler indicates that it is not possible since the group is not FAST managed. This message is seen in Figure 91.
Unisphere for PowerMax and Solutions Enabler both provide viewable compression metrics for devices. Figure 92 includes a view where the compression ratio of the device is shown. In this case, the data is being compressed 5.0 to 1.
Using Solutions Enabler, it is also possible to obtain this information. Figure 93 shows how to list the data reduction metrics for an individual device that is part of a storage group with data reduction enabled.
Note: All supported data services, such as SnapVX, SRDF, vVols, and encryption (D@RE) are supported with data reduction.
Customer applications are one of the biggest factors that can impact data reduction ratios. For example, if the application can compress data before storing it, the PowerMax is unlikely to compress it further. Oracle Compression is a good example of a feature of the Oracle Database that benefits little from array data reduction. Similarly, software that encrypts data before storing it on the array cannot take advantage of the deduplication capability of array data reduction. Therefore, features such as these may guide placement of devices in storage groups without data reduction enabled.