/******************************************************************************
* Create a degraded read DAG for RAID level 1
*
* Hdr -> Nil -> R(p/s)d -> Commit -> Trm
*
* The "Rd" node reads data from the surviving disk in the mirror pair
* Rpd - read of primary copy
* Rsd - read of secondary copy
*
* Parameters: raidPtr - description of the physical array
* asmap - logical & physical addresses for this access
* bp - buffer ptr (for holding write data)
* flags - general flags (e.g. disk locking)
* allocList - list of memory allocated in DAG creation
*****************************************************************************/