HP Cisco MDS 9124 Cisco MDS 9000 Family Fabric Manager Configuration Guide, Re - Page 971

Chapter 48 Configuring FCIP Using the FCIP Wizard Send documentation comments to [email protected] Figure 48-25 Backup Server FCIP Link Tape Acceleration for Write Operations MDS with IPS MDS with IPS WAN Tape Drive FC Write Command 1 Status 1 Write Command 1 Write Command 1 Status 1 Write Command N Write Command N Status N WRITE FILEMARKS operation Write Command N Status N WRITE FILEMARKS operation WRITE FILEMARKS status 120492 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 SAN-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 SAN-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. OL-16184-01, Cisco MDS SAN-OS Release 3.x Cisco MDS 9000 Family CLI Configuration Guide 48-33