Cisco Cisco MDS 9000 I O Accelerator Guia De Informação
Q&A
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Cisco MDS 9000 I/O Accelerator
Q.
What is the Cisco
®
MDS 9000 I/O Accelerator (IOA)?
A.
The Cisco MDS 9000 IOA feature is a solution for accelerating disk and tape I/O operations, including disk and
tape write and tape read I/O operations, to mitigate the effects of latency.
Q.
What other acceleration solutions were available prior to IOA?
A.
Other acceleration solutions include:
●
Fibre Channel over IP (FCIP) Write Acceleration (FCIP-WA) and Tape Acceleration (FCIP-TA) on the Cisco
MDS 9000 18/4-Port Multiservice Module (MSM) and 9222i Multiservice Modular Switch (MMS)
●
Fibre Channel Write Acceleration (FC-WA) on Cisco MDS 9000 Storage Services Modules (SSMs)
Q.
Why use IOA?
A.
IOA provides a unified and comprehensive acceleration service that is transport and speed agnostic. IOA
delivers disk write acceleration and tape acceleration in a highly scalable and available service. It has the
following unique characteristics:
●
Transport agnostic: It works independent of the type of data center interconnect (DCI). It supports Fibre
Channel and Fibre Channel over IP (FCIP) and has been designed to support Fibre Channel over Ethernet
(FCoE).
●
Speed agnostic: It works independent of DCI link speed. It supports 1/2/4/8/10-Gbps Fibre Channel and
Gigabit Ethernet and has been designed to support 16-Gbps Fibre Channel.
●
Highly available and scalable:
◦
It supports multipath connectivity for DCI over PortChannels and Equal-Cost Multipath (ECMP), to enhance
link availability of the DCI.
◦
Lightweight Reliability Transport Protocol (LRTP) developed by Cisco provides resiliency after Inter-Switch
Link (ISL) failures, thereby protecting the application against planned and unplanned metropolitan-area
network (MAN) and WAN ISL failures.
◦
Engine clustering protects against acceleration and compression engine failures by reassigning flows on
the failed devices to other engines.
◦
Multipath and clustering support makes IOA scalable, providing the flexibility to dynamically increase DCI
bandwidth and acceleration capacity.
Q.
What is LRTP and how does IOA provide resiliency after ISL failure?
A.
Lightweight Reliability Transport Protocol, or LRTP, is a proprietary Cisco protocol that provides reliability and in-
order delivery for IOA flows. It provides TCP-like reliability and retransmission capabilities with complex
semantics and congestion-control mechanisms. LRTP recovers from packet loss due to ISL failure and from
reordered packets due to natural delay variances over the various ISLs in PortChannels or over ECMP. End
applications such as tape backup and remote replication are unaware of transient packet loss due to ISL
failures.
Note that the objective of LRTP is not to solve persistent drops in Fibre Channel networks as TCP does for IP
networks, but instead to handle out-of-order frames and lost frame retransmissions.
Note also that TCP retransmission will still occur for the FCIP links in the IP network. However, the LRTP
retransmission interval is greater than that for TCP.