来讨论一个recovery的问题

jayciedede · 发表于 2008-11-10 10:10

如果已经存在一个空库的话，再用lvcopy的话，这个库是可以用的。
是不是数据库建立的时候会在操作系统登记某些信息，如果直接copy的话就不登记了？
奇怪，但是oracle直接文件拷贝的是可以的，前提是自己先手工建好实例。

wangzhonnew · 发表于 2008-11-10 10:58

as what suggested by unixnewbie, copying file is OKAY if IO Suspend has been fired. The problem is, why DB2/Oracle doesn't support the backup/recovery strategy for FS consistence-group backup when database is online and transactions are running.

(don't argue with me that you tried to backup FS for a SAMPLE database when it's online and few application running, yeah i know sometime it will be able to get you a usable database by crash recovery. But officially both ibm/oracle does NOT support the backup strategy when the database is online and applications are writing into it)

DB2Viper · 发表于 2008-11-10 11:29

我以为，应该是os不像数据库那样有一个一致点的概念。纯粹猜的

wangzhonnew · 发表于 2008-11-10 11:59

FlashCopy consistency groups can be used to help create a consistent point-in-time copy across multiple volumes, and even across multiple ESSs, thus managing the consistency of dependent writes. This tip discusses an example of how to do it when using FlashCopy.
http://www.redbooks.ibm.com/abstracts/tips0309.html?Open

basically it's similar with IO Suspend from DBMS level, it's freezing the write activity cross all FS in the consistency-group and do flash copy, then resume all I/O...

so why db2/oracle still doesn't support the backup/recovery strategy based on this?

macrozeng · 发表于 2008-11-10 19:32

呵呵，wangzhonnew 提出了一个很好的问题，随便谈谈自己的想法先

我个人认为 FlashCopy 和 db2 Suspended I/O 还是有很多不同的， FlashCopy 是保持一致组里面的所有文件到某个时间点的一致，而在执行 FlashCopy 阶段，数据库状态应该是不可用的（因为所有文件（包括日志）都不能更新了），这就导致了数据库不能连续工作了。这就导致了这种方式不可能作为一种通常备份的方式。

而 db2 Suspended I/O 只是把表空间的状态更改，使其表空间可以保持相对一致，然后把所有变化记录到日志里面去。