Cisco AP776A - Nexus Converged Network Switch 5020 Configuration Manual page 1025

Chapter 41 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
Figure 41-14
Backup
Server
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.
Note
The Cisco NX-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 NX-OS software.
In an example of tape acceleration for read operations, the restore server in
operations to a drive in the tape library. During the restore process, the remote Cisco MDS switch at the
tape end, in anticipation of more SCSI read operations from the host, sends out SCSI read operations on
its own to the tape drive. The prefetched read data is cached at the local Cisco MDS switch. The local
Cisco MDS switch on receiving SCSI read operations from the host, sends out the cached data. This
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 read acceleration for tapes. This improves the performance for tape reads
on WAN links.
OL-18084-01, Cisco MDS NX-OS Release 4.x
FCIP Link Tape Acceleration for Write Operations
MDS with
IPS
Write Command 1
Status 1
Write Command N
Write Command N
Status N
WRITE FILEMARKS operation
WRITE FILEMARKS status
In some cases such as a quick link up/down event (FCIP link, Server/Tape Port link) in a tape
library environment that exports Control LUN or a Medium Changer as LUN 0 and tape drives
as other LUNs, tape acceleration may not detect the tape sessions and may not accelerate these
sessions. The workaround is to keep the FCIP link disabled for a couple of minutes before
enabling the link. Note that this does not apply to tape environments where the tape drives are
either direct FC attached or exported as LUN 0.
MDS with
IPS
WAN
Write Command 1
Write Command 1
Write Command N
WRITE FILEMARKS operation
Cisco MDS 9000 Family CLI Configuration Guide
Tape
Drive
FC FC
Status 1
Status N
Figure 41-15
Configuring FCIP
issues read
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