dp配置备份数据库configure时如下错误

jingweixy

dp配置备份数据库configure时如下错误：（以前是备份成功的，上周有个磁带坏了，就没有备份成功过）

Recovery Manager: Release 10.2.0.2.0 - Production on Fri Aug 28 08:53:19 2009

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

RMAN>
connected to target database: ERPDB (DBID=4069759595)
using target database control file instead of recovery catalog

RMAN> 2> 3> 4>
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of allocate command on dummy channel at 08/28/2009 08:53:22
ORA-19554: error allocating device, device type: SBT_TAPE, device name:
ORA-27000: skgfqsbi: failed to initialize storage subsystem (SBT) layer
Additional information: 7110
ORA-19511: Error received from media manager layer, error text:
   SBT error = 7110, errno = 0, sbtinit: internal error - invalid argument(s)

RMAN>

Recovery Manager complete.

jingweixy

dp 中的import,export,recycle都是什么意思，什么情况下用呢？
请大师指导