Oracle Backup on Raw File Systems

[Shivkumar]

Dear Sirs,

I suppose that Oracle 9i RAC ADR are usually installed under RAW file system under MC Serviceguard
clustering. I understand that Oracle is installed on Raw File System for best i/o throughput. Someone told that backup can't be taken using backup software tools if any software is installed on raw file systems.

What are the problems with the raw file systems ?

Thanks,
Shiv

[Bill Hassell · Accepted solution]

There is no such thing as a raw filesystem. It is called raw because data is stored in specific blocks as defined by Oracle. You can't examine these data elements except using Oracle. So there is nothing to backup (with conventional tools like cpio, tar and fbacku), just a stream of binary data. Now someadmins will use dd but dd has no directory, no timestamp when the backup was taken and no index or verification of the backup.

Raw data volumes are also VERY easy to destroy when sysadmins do not communicate among each other. The raw volumes look as if they are not used and an admin looking for space might issue an lvremove on one of these non-filesystem volumes.

This means that you MUST choose a reliable backup product that is designed for raw volumes. While there might be some freeware tools that improve on dd, you need extensive tools to document where and when backups have been taken of your raw volumes. Data Protector (from HP) is a good choice, other commercial backup tools also support raw volumes. Your backup program is just as important as the data you are storing. Redcovering raw volumes without professional tools may take days of consulting.

[A. Clay Stephenson]

What he said.

Don't let anyone talk you into using dd; it's the only standard utility that you can use but there is no way to test the validity of the backup and no recovery on errors. You have the option of Data Protector or RMAN or better still -- use cooked file with Oracle RAC. That is possible with the new Cluster Filesystem (CFS). The performance is good and it looks like a big filesystem to all the hosts. That would be my approach.

[John Payne_2]

Shiv,

There was a fairly good discussion about this 2 weeks ago. http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=990479
The only Oracle disasters I know about (at least second hand...) where data was actually lost involved raw disk. (3 separate cases.) Our DBA's bring up the topic of raw disk about once every 3 years, and we always end up changing their thinking so they stay on so called "cooked" disk.

I just barely went through this again with them a month ago. It turns out they wanted to test a tool Oracle developed which only used raw disk. After digging up all the charts (Even from Oracle's website), and explaining our position, they went back and talked about things again. They made some calls to Oracle, and Oracle indicated that the tool they wanted to test would very soon support "cooked" disk. We are all happily in agreement again that raw disk is not the way to go in our environment. (At least until Dec 2008... ;) )

Hope it helps

John

[Yogeeraj_1]

hi shiv,

the best possible and reliable way to backup your oracle database indepently of it being on raw or cooked file system is to use RMAN.

dd was used in the old days to backup Oracle databases on raw devices. With RMAN, this way of backup has been obsoleted.

Also, the ORACLE has a new way of managing storage - ASM. Read about it.

hope this helps too!

kind regards
yogeeraj

[Shivkumar]

What is "cooked file system" ? is it some new file system on hpux system ?

[Devender Khatana]

Hi Shiv,

Coocked File System means a normal file system where as raw device means a LVOL without a file system.

While creating lvol you can leave it as it is like

#lvcreate -L 500 -n raw_data /dev/vgxx

It will create a LVOL which can be used as raw space by an application.

Whereas creating a file system on this LVOL will make it cooked by

#newfs -F vxfs /dev/vgxx/raw_data

HTH,
Devender