raw file for data warehouse

[abhijit]

Hi All,

I need to know what factors determin use of raw file over unix file system. Pros and corns of both the file systems.

My Environment:

HP-UNIX 11.00; Oracle8.1.7; 4CPU, each of 512 MB
Data warehouse application: table size of biggest one is 200GB

Appreciate your valuable feedback/link to web in advance.

Regards,

abhijit

[pwoneill]

Check out [url]http://vc.itec.suny.edu/itec/oracle/unixbulletins/rawdev.html[/url]

[abhijit]

Thanks for your reply. I will go thru' it. I will get back to this thread, if I see something.

Regards,

abhijit

[DBAtrix]

I used them at my last company they were a pain to manage. I would want some real benchmarking tests before having to hassle with them. If you do get, be sure you can check some basic info about them to troubleshoot with, like how to determine the size (it's not very straightforward). You have to check your control file size to make sure they don't write off the end of the device.

D.

[wjramsey]

I believe that one of the issues can be that some systems cannot do asynchronous io on cooked filed systems. I know this is the case with Data General. The only way to do asychronous I/O is to use raw partitions. You should consult with your vendor to see if this is the case.

I've heard conflicting stories about the advantages of using RAW these days with some of the newer filesystem types.

Anyone else care to weigh in on the subject. I'd be interested in hearing some views from people using RAW. Personally I've never had the displeasure of having to manage them.

Joe

[abhijit]

Yeah! it's looks very complex to me and make me difficult to take decision. Can I have some of my files raw and rest UFS. I have full authority to play with disk configuration since I am very closely working with Sys Admin.

DBAtrix: "You have to check your control file size to make sure they don't write off the end of the device. "

What do you meant by that...I didn't get that point...Since contorl file reside in sys. tablespace I have to take care sys. tablespace only. More over, it's contol file or any file, I have to see that respective tablespace does not run out of space.

Joe: HP-UX can support asynchronous I/O.

Hope to hear more feedback on this context.

Regards,

abhijit

[DBAtrix]

2 points to address here.

1. Control files are *not* in sys tablespace; they are in the location specified in your init.ora file with control_files parameter.

2. It's quite easy to determine when your tablespace is about to fill up. And if a user tries to exceed the datafile (assuming no autoextend since these are raw devices), no real harm is done other than a failure to extend a segment. However, controlfiles grow, and the size of the control file is not stored anywhere in the database (that I know of). So you can't tell how long the controlfile is. If the controlfile grows past the end of the device, very bad things happen to DBAs (usually requiring a restore & recovery).

On MetaLink, see Note:73584.1
Subject: How to determine exact size of a controlfile on a raw device

As far as mixing raw & UFS I think you can, altho some Parallel server configurations might limit your choices.

hope that clears some things up.

d.