Cisco MDS 9000 series Configuration Manual page 53

Chapter 2 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 2-14
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.
In some cases such as a quick link up/down event (FCIP link, Server/Tape Port link) in a tape library
Note
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. You need to
keep the FCIP link disabled for a couple of minutes before enabling the link. This does not apply to tape
environments where the tape drives are either direct FC attached or exported as LUN 0.
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-19525-01,Cisco MDS NX-OS Release 4.2(1)
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
MDS with
IPS
WAN
Write Command 1
Write Command 1
Write Command N
WRITE FILEMARKS operation
Cisco MDS 9000 Family NX-OS IP Services Configuration Guide
Tape
Drive
FC FC
Status 1
Status N
Figure 2-15
Configuring FCIP
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