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48-33
Cisco MDS 9000 Family Fabric Manager Configuration Guide
OL-17256-03, Cisco MDS NX-OS Release 4.x
Chapter 48 Configuring FCIP
Using the FCIP Wizard
Figure 48-25 FCIP Link Tape Acceleration for Write Operations
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 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.
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 Figure 48-26 issues read
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.
FCFC
Backup
Server
MDS with
IPS
MDS with
IPS
Tape
Drive
Write Command 1
Write Command 1
Write Command 1
Write Command N
Write Command N
Write Command N
Status 1 Status 1
Status N
Status N
WAN
WRITE FILEMARKS status
WRITE FILEMARKS operation
WRITE FILEMARKS operation
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