• When reading a block, the RACF® manager first searches the in-storage buffers for a valid copy of the block. If it finds one, it uses it. If it does not find a valid copy, the RACF manager obtains an in-storage buffer from the pool of buffers, reads the data block into that buffer, and retains the data block in storage after the I/O operation.
• When updating a block, the RACF manager searches the in-storage buffers for a copy of the block. If it does not find one, it obtains an in-storage buffer from the pool of buffers.

  When a block is updated, RACF always performs an I/O operation so that the RACF database has an up-to-date version of that block.

When getting a buffer from the pool, the RACF manager attempts to get a buffer that is empty or contains an out-of-date block. (A block is only out-of-date in a shared database system.) If it finds none, the manager takes the buffer containing the least-recently used block.