IBM DS8880 Series Introduction And Planning Manual page 189

when the request is media related. This control switch determines whether
SIMs are sent to all, or to only the first, attached IBM Z LPAR making an
I/O request to the logical system or logical volume.
IBM Z high-performance FICON enhanced buffer management
IBM Z high-performance FICON enhanced buffer management provides
improved performance for multi-site configurations when writing data
remotely (remote site recovery).
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Chapter 7. Storage complex setup