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Chapter 33
Configuring FCIP
S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m .
Write acceleration cannot be used across FSPF equal cost paths in FCIP deployments. Native Fibre
Note
Channel write acceleration can be used with Port Channels. Also, FCIP write acceleration can be used
in Port Channels configured with channel mode active.
Caution
FCIP write acceleration with FCIP ports as members of PortChannels in Cisco MDS SAN-OS Release
2.0(1b), and later, are incompatible with the FCIP write acceleration in earlier releases.
To enable write acceleration, follow these steps:
Command
Step 1
switch1# config terminal
switch(config)#
Step 2
switch1(config)# interface fcip 51
switch1(config-if)#
Step 3
switch1(config-if)# write-accelerator
switch1(config-if)# no write-accelerator
FCIP Tape Acceleration
Tapes are storage devices that store and retrieve user data sequentially. Applications that access tape
drives normally have only one SCSI WRITE operation outstanding to it. This single command process
limits the benefit of the write acceleration feature when using an FCIP tunnel over a long-distance WAN
link. It impacts backup and archive performance because each SCSI WRITE operation does not complete
until the host receives a good status response from the tape drive.
The FCIP tape acceleration feature helps solve this problem. It improves tape backup and archive
operations by allowing faster data streaming from the host to the tape over the WAN link.
The backup server in
for the remote tape drives, the local Cisco MDS switch proxies a transfer ready to signal the host to start
sending data. After receiving all the data, the local Cisco MDS switch proxies the successful completion
of the SCSI WRITE operation. This response allows the host to start the next SCSI WRITE operation.
This proxy method results in more data being sent over the FCIP tunnel in the same time period
compared to the time taken to send data without proxying. The proxy method improves the use of WAN
links.
At the tape end of the FCIP tunnel, another Cisco MDS switch buffers the command and data it has
received. It then acts as a backup server to the tape drive by listening to a transfer ready from the tape
drive before forwarding the data.
The Cisco SAN-OS provides reliable data delivery to the remote tape drives using TCP/IP over the WAN.
It maintains write data integrity by allowing the WRITE FILEMARKS operation to complete end-to-end
without proxying. The WRITE FILEMARKS operation signals the synchronization of the buffer data
with the tape library data. While tape media errors are returned to backup servers for error handling, tape
busy errors are retried automatically by the Cisco SAN-OS software.
The tape acceleration feature is disabled by default and must be enabled on both sides of the FCIP link.
Note
If it is only enabled on one side of the FCIP tunnel, the tunnel is not initialized.
OL-6973-03, Cisco MDS SAN-OS Release 2.x
Figure 33-9
issues write operations to a drive in the tape library. Acting as a proxy
Purpose
Enters configuration mode.
Creates an FCIP interface (51).
Enables write acceleration.
Disables write acceleration (default).
Cisco MDS 9000 Family Configuration Guide
Advanced FCIP Features
33-21
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