As erasure coding, DDP provides dual parity for 6D+2P and 14D+2P protection schemes. DDP groups are built on the drives, and pools are built on the DDP groups. DDP starts at any number of drives, each of which includes spare area. That is, instead of distributing added data on a single spare area, the data is distributed to spare capacity across all drives. A spare or unused drive is not required. The capacity of the spare area is reserved internally, and the minimum number of drives in the configuration is the RAID width plus one. Therefore, the capacity of the spare area cannot be reduced.
Any number of drives with the RAID width (the number of data and parity drives in the RAID level) plus one or more drives can be accommodated. Therefore, a DDP group can be configured with the optimal number of drives to accommodate the required data capacity, and the drives can be installed in the drive slots efficiently. Additional drives can be added one at a time rather than in groups of drives. As new drives are added, the storage system reallocates the spare capacity across all of the drives. It's not possible to write a single block of data to a single drive. And as the space on the drives reaches maximum capacity, the system has to open up capacity on all drives before new data can be written.
If a drive failure occurs, the workload is spread across all the drives, which results in stable conditions and faster rebuilds. The stable I/O performance is provided even during rebuild and data redistribution processing by adjusting I/O operations and rebuild and redistribution I/O operations. All drives can be accessed equally even during collection processing in the event of a drive failure, and therefore the performance deviations are reduced.
DDP groups belong to DP pools, and are managed in the same way as pools with RAID groups. These DP pools support only DRS-VOLs and journal volumes. DDP does not support non-data-reduced thin provision volumes.
DDP groups created through the CCI or REST API afford a greater degree of granularity than DDP groups created through VSP One Block Administrator. With VSP One Block Administrator, you can only increase logical drives, not create specific configurations.