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File System vs Raw Device for Oracle

Miguel Angel Aliaga_1
Occasional Advisor

File System vs Raw Device for Oracle

actually we are working with a 400GB OLTP Oracle database on raw device ( Oracle 8.1.7.x ) and we want to know about opinions of using raw devices or to migrate to file systems.


A. Clay Stephenson
Acclaimed Contributor

Re: File System vs Raw Device for Oracle

I've done these measurements and these are my conclusions ON MY DATA.

If you are running HP-UX 10.20 or 11.0, the best performance (essentially indistinguishable) from RAW/IO is obtained
using OnlineJFS mount options delaylog,nodatainlog,convosync=direct,mincache=direct for data files and indices. Redo and archive logs should be delaylog,nodatainlog.

The convosync=direct,mincache=direct option bypass the UNIX buffers and thus you are in essence raw/io. Typical maximum buffer cache size should be around 300MB. I find that setting a fixed buffer cache using bufpages is slightly better.

On 11.11, I've actually found that fully buffered I/O is the better performer. All files should be set to nodatainlog,delaylog AND increase buffer cache to about 900-1000MB.
The dynamic buffer cache routines are much improved in 11.11 so feel free to use them although for the present I'm stubbornly sticking to a fixed buffer cache but I've really not been able to measure any difference between reasonable dynamic buffer cache settings and good fixed buffer cache settings on my boxes.


Of course, the real answer is to do the measurements yourself on your box and using your data.

Don't overlook that maintenance (backups, restores, snapshots) is a very important factor as well; in that sense, filesystems win hands down.

If it ain't broke, I can fix that.
Leif Halvarsson_2
Honored Contributor

Re: File System vs Raw Device for Oracle

Sridhar Bhaskarla
Honored Contributor

Re: File System vs Raw Device for Oracle

I agree that using Online JFS options particularly mincache=direct and convosync=direct bypass the buffers. 'mincache' takes care of non-synchronous writes while convosync takes care of 'synchronous' writes. I prefer to use filesystems with these options instead raw devices.

Quick IO and blocklevel backups from veritas seem to offer better performance but I haven't tried them yet.

Not to ignore, striping also can be considered to improve the performance and load balancing.

You may be disappointed if you fail, but you are doomed if you don't try
Honored Contributor

Re: File System vs Raw Device for Oracle