Each TCP/IP stack allocates 64-bit fixed private staging buffer memory for outbound Shared Memory Communications over RDMA (SMC-R) data. Staging buffers are not associated with specific SMC-R links or link groups, but are used by all TCP connections that traverse SMC-R links on this stack.
Like remote memory buffers (RMBs), staging buffers are 1 MB in length and must be registered with the IBM® 10GbE RoCE Express® interface before they are used for SMC-R communications. Unlike RMBs, the address of the staging buffer is not shared with the remote SMC-R peer because only local applications access the staging buffer storage.
z/OS® Communications Server allocates 4 MB of staging buffer storage when the first 10GbE RoCE Express interface is activated, and allocates more buffers as necessary to accommodate application workloads.