For a Vmax, we are defining a mainframe environment on 400GB FC HDAs, with a RAID 5 (7+1) configuration. Being allotted eight array groups or 64 HDAs, I am told that I can expect to have 21.51 TBs of useable space to configure. It was explained like this to me.
Each 400 GB HDA formatted as a CKD device yields approximately 382 GBs of useable space. With 64 HDAs, my raw capacity is 64 * 382 GBs or 24448 GBs. The useable RAID 5 capacity is 88% of the raw capacity or 21514 GBs (24448 * .88). The parity for RAID 5 is handled with track level protection.
I am old school and would have estimated my configuration to be 7 data and 1 parity. Therefore, I expected to have 18824 GBs of useable space.
How does parity for RAID 5 work with track level protection?