A transaction generator generates memory transactions identical to processor memory transactions to initialize, rebuild, and verify memory added or replaced during operation of a computer system configured for RAID memory. The transactions read and rewrite the correct value for replaced memory and write a known good value for added memory. Memory writes are verified by a read after the write transaction. The transaction generator is a state machine. A first counter is used for holding memory addresses of the transactions, automatically incrementing after each transaction. A second counter can throttle the generation of transactions by controlling the incrementation speed of the first counter. Transactions generated by the transaction generator have a transaction identifier, selected from a pool of available transaction identifiers. The transactions can complete out of order.