A P P E N D I X A Scsi Write Acceleration And Tape Acceleration - Cisco MDS 9000 series Configuration Manual

Appendix A SCSI Write Acceleration and Tape Acceleration
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
response allows the host to start the next SCSI WRITE operation. This proxy method results in more
data being sent over the FCIP or Fibre Channel tunnel in the same time period compared to the time taken
to send data without proxying. The proxy method improves the performance on WAN links.
Figure A-2
Backup
Server
Write Command 1
Write Command N
At the tape end of the FCIP or Fibre Channel 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 NX-OS provides reliable data delivery across 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 or FC 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-20708-01, Cisco MDS NX-OS Release 5.0(1a)
SCSI Tape Acceleration for Write Operations
MDS with
IPS
Write Command 1
Status 1
Write Command N
Status N
WRITE FILEMARKS operation
WRITE FILEMARKS status
MDS with
IPS
WAN
Write Command 1
Status 1
Write Command N
Status N
WRITE FILEMARKS operation
Cisco MDS 9000 Family I/O Accelerator Configuration Guide
SCSI Tape Acceleration
Tape
Drive
FC FC
Figure A-3 issues read
A-3