McDATA 3000 Manual Do Utilizador

 

 

This chapter provides an overview on FC/SCSI Tape Pipelining 
(Device Extension), LUN discovery, and dynamic and static mapping.

FC/SCSI Tape Pipelining on the UltraNet Edge 3000 allows tape 
backup performance over distances up to thousands of miles. It 
performs over long distances without the distance performance 
penalty found in non-pipelined operations. 

FC/SCSI Tape Pipelining uses device emulation as the means to 
extend the devices from one end of the network to the other. The 
following sections discuss how buffering, emulation and error 
recovery work. 

Before addressing the impact of device emulation on tape backup, it 
is helpful to understand how buffered devices operate when natively 
attached to a server.

The concept of buffering was developed primarily to increase 
performance between a server and a device’s control unit.

Upon receiving a command from the server, non-buffered devices 
need to complete the command in its entirety prior to acknowledging 
completion to the server. While this synchronous method of data 
transfer is very safe from a command completion perspective, it 
creates I/O performance issues for the server by tightly coupling each 
command completion to overall completion of the host I/O transfer.