Cisco MDS 9000 series Configuration Manual page 96

SCSI 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
Figure A-3
Restore
Server
Read command N+1
The Cisco NX-OS provides reliable data delivery across the WAN. While tape media errors during the
read operation are returned to the restore server for error handling, the Cisco NX-OS software recovers
from any other errors.
In tape acceleration for writes, after a certain amount of data has been buffered at the remote Cisco MDS
switch, the write operations from the host are flow controlled by the local Cisco MDS switch by not
proxying the Transfer Ready. On completion of a write operation when some data buffers are freed, the
local Cisco MDS switch resumes the proxying. Likewise, in tape acceleration for reads, after a certain
amount of data has been buffered at the local Cisco MDS switch, the read operations to the tape drive
are flow controlled by the remote Cisco MDS switch by not issuing any further reads. On completion of
a read operation, when some data buffers are freed, the remote Cisco MDS switch resumes issuing reads.
The default flow control buffering uses the automatic option. This option takes the WAN latencies and
the speed of the tape into account to provide optimum performance. You can also specify a flow control
buffer size (the maximum buffer size is 12 MB).
Cisco MDS 9000 Family I/O Accelerator Configuration Guide
A-4
SCSI Tape Acceleration for Read Operations
MDS with
IPS
Read command N
Read data N
Status N
Status N+1
Appendix A
MDS with
IPS
WAN
Read command N
Read data N
Status N
Read command N+1
Read data N+1
Status N+1
Read command N+2
SCSI Write Acceleration and Tape Acceleration
Tape
Drive
FC FC
Read data N
Status N
Status N+1
OL-20708-01, Cisco MDS NX-OS Release 5.0(1a)