> # FCIP Write Acceleration

> The FCIP write acceleration feature enables you to significantly improve application write performance when storage traffic is routed over wide area networks using FCIP. When FCIP write acceleration is enabled, WAN throughput is maximized by minimizing the impact of WAN latency for write operations.

> Note The write acceleration feature is disabled by default and must be enabled on both sides of the FCIP link. If it is only enabled on one side of the FCIP tunnel the write acceleration feature will be turned operationally off.

> Note IBM Peer to Peer Remote Copy (PPRC) is not supported with FCIP write acceleration.

> The WRITE command ,without write acceleration requires two round-trip transfers (RTT), while the WRITE command with write acceleration only requires one RTT. The maximum sized Transfer Ready is sent from the host side of the FCIP link back to the host before the WRITE command reaches the target. This enables the host to start sending the write data without waiting for the long latency over the FCIP link of the WRITE command and Transfer Ready. It also eliminates the delay caused by multiple Transfer Readys needed for the exchange going over the FCIP link.

> Tip FCIP write acceleration can be enabled for multiple FCIP tunnels if the tunnels are part of a dynamic PortChannel configured with channel mode active. FCIP write acceleration does not work if multiple non-PortChannel ISLs exist with equal weight between the initiator and the target port. Such a configuration might cause either SCSI discovery failure or failed WRITE or READ operations.

> Tip Do not enable time stamp control on an FCIP interface with write acceleration configured.

> Note Write acceleration cannot be used across FSPF equal cost paths in FCIP deployments. Native Fibre Channel write acceleration can be used with PortChannels. Also, FCIP write acceleration can be used in PortChannels configured with channel mode active or constructed with PortChannel Protocol (PCP).

> Caution | In Cisco MDS SAN-OS Release 2.0(1b) and later and NX-OS Release 4.x, FCIP write acceleration with FCIP ports as members of PortChannels are not compatible with the FCIP write acceleration in earlier releases.

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