DUL是Oracle内部恢复工具，由Oracle新西兰工程师bernard.van.duijnen 开发，是使用C语言开发的，在不同平台上会使用不同的binary文件。
由于bernard.van.duijnen 开发DUL的时候使用了一些Oracle数据库的内核头文件（主要是一些.h)文件，所以在Oracle来说DUL是需要被严格控制的，因为DUL直接用了Oracle数据库的源代码，属于Oracle知识产权的一部分。
早期DUL是不加锁的，后来变成加日期锁，就是说 好比bernard.van.duijnen 在10月1日发布了一个版本，日期锁是30天，那么这个版本到11月1日基本就失效了， DUL不是简单的读OS时间，所以改OS时间是没用的。 因为Oracle的datafile里也记录了一个当前时间，所以DUL读的是datafile里的时间。 一般用户不可能为了用DUL去改那个时间。
同时早期的Oracle DUL版本用在现在的版本10g、11g、12c的数据库桑基本是用不了了，因为太老了。 在美国使用DUL是被严格控制的，在中国国内的话 基本就是Oracle ACS 高级客户服务部门对外在用，购买ORACLE ACS现场服务的价格还是很贵的。
回过头来介绍下Oracle PRM， ORACLE PRM是诗檀软件parnassusdata.com 用java 语言开发的， 在DUL基础上加了图形化界面GUI，它们的目标大概是做一个易用的DUL。
由于是JAVA语言开发 ，所以要求运行时有JAVA环境，这个ORACLE 10g自带了JDK 1.4.2，所以它们的程序 只要有ORACLE的地方大概都可以跑， 不过它们推荐至少用JDK 1.6以上版本，大概是因为JDK 版本低 程序会有点问题。
这个ORACLE PRM是对外可以下载的，下载下来是社区版， 就是阉割的版本，只能抽取一万行数据出来。 它们的无限制的版本叫企业版，价格是7500人民币。
不过ORACLE PRM有个ASM文件克隆的功能是免费的，可以直接从坏掉的ASM DISKgroup里抽数据文件，这个功能还不赖，叫ASM FILE CLONE。
Why ParnassusData Recovery Manager PRM is necessary?
Isn't RMAN enough for ORACLE database recovery? Why developping PRM for Oracle recovery?
In modern growing IT systems, database size is growing geometrically. Oracle DBAs are facing the problem that disks are insufficient for full backup, and tape storages take much more time than usual expectation.
Truth been told, "Database, backup 1st" is the first lession for DBAs, however that fact is : backup disk not sufficient, storage not on time, even the backup image does now work.
In order to solve the above problems, PD Recovery Manager integrates the algorithm in Oracle database data structure, boot process which can solve system table lost, data dictionary error, and storage corruption impaction. In addition, it can also recovery the data from Truncate/Delete mistake.
No matter you are a profesional DBA or new fish in Oracle world, you can master this user friendly tool immediately. PRM is easy to install and use. You don't need to have any Oracle deep knowledge or skill in scripts, but just click by click finishing all recovery process.
Comparing the traditional recovery tool like Oracle DUL which is an Oracle internal tool and only for Oracle employee usage. PRM can be use for any kind of IT professionals or geeks. It saves time, decreases the recovery falure, and cuts down the total cost of enterprise.
There are 2 modes for data recovery:
By traditional way, data has to be extract to text file and then insert to new DB by SQLLDR tools, which takes double time and ocupies double storage size.
ParnassusData Recovery Manager integrates data bridge function, which can extract data from orginal source and insert into new destination without any intermedia. This is a truly time and storage saver.
Oracle ASM is becoming popular in enterprise database implementation, due to its advantage in high performance, cluster support, and easy administration. However, for many IT professionals, ASM is a black box. Once ASM occurs error in DiskGroup mounting, it means that all data is locked in ASM. In this circumstance, without PRM, only senor Oracle experts can fix ASM internal structure which is also a problem for oracle normal user.
PRM now can support two kinds of ASM data recovery：
Once Disk Group can not MOUNT, PRM can read metadata, and extract ASM file from Disk Group
Once Disk Group can not MOUNT, PRM can read ASM file and extract data which supports data export and data bridge 2 modes
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