Old debate: Raw Device Vs. File System

[Jean-Luc Oudart]

Filipe,

the powerPoint presentation is dated Feb'98 I guess vxfs may have improved since.

If the test program is available, has anybody run this test on HPUX 11.0 11i ?
What are the results ?

In SEP's thread I was wondering if redo on raw would be a good choice (this is as I do not have OnlineJFS). I suppose the choice is much clearer for you.

Jean-Luc

[Todd McDaniel_1]

Hey,

I found some more my DBA sent me... I can give you the metalink IDs and post them here...


Doc ID: Note:37914.1 and Note:29676.1

[Wim Rombauts]

Filipe,

As you can read in the previous entries : using a filesystem for Oracle datafiles does not really bring performance down, and it gives you a lot of flexibility : autoextending datafiles, cold backups, a lot of filesystem management tools, ...

The only reason I see to ise RAW device files, is when you plan to use oracle RAC in the future, because that is only supported on raw device fies.

I am using oracle RAC and thus need raw device files, and I think raw device files are a serious disadvantage in managebility and flexibility. Sometimes I still dream about the days before RAC made everything more difficult.

[Christian Gebhardt]

hi

to Wim:
we have built an Oracle RAC on Solaris 2.9 with "Veritas DBE/AC for Oracle RAC,Version 3.5". This Package from Veritas allows you to build an Oracle RAC on Filesystems.

We tested RAC on Solaris 2.9 with Solaris Cluster 3.0 on Raw Device and there was no measurable difference.

Details:
Oracle 9.2.0.4, 4 Nodes in 2 locations (about 14 km distance), EMC L1000 on both sides, Size of the database 100GB.

Chris

[Mobeen_1]

Filipe,
You have bought to the forefront a discussion which i deem interesting.

Please review the link below for some advantages of filesystems
http://oss.sgi.com/projects/xfs/papers/xfs_white/xfs_white_paper.html

The following is what Oracle thinks :-)

Raw Devices vs. Filesystems
---------------------------
When possible, advanced file systems such as xfs, jfs, or vxfs should be preferred over ufs file systems. This is to utilize the improved journal and performance features (such as elimination of double buffering) that advanced file systems offer over ufs. It must be noted that if you configure your system using ufs file systems the necessary file system level parameters need to be configured and tuned, as the default values will not provide optimal performance.
When using Veritas vxfs file systems, Quick I/O can provide raw device comparable performance without losing the benefits of a file system. This is because the Quick I/O driver intercepts all DBWR writes (when enabled) thus bypassing the file system buffer cache. This provides raw device comparable performance, as the classic problems of double buffering and wasted CPU
cycles in managing the file system buffer cache are avoided. When using other types of advanced file systems, Direct I/O can be preferred if supported by the OS, as it too provides raw device comparable performance. The use of raw devices does not add any significant value when compared to advanced file systems with Quick/Direct I/O drivers (wherever applicable).
Raw devices do add a level of operational complexity without justifiable performance benefits, when compared to advanced file systems configured with Veritas Quick I/O or Direct I/O (supported by the OS). In these cases, the configuration and use of raw devices should be reserved for Oracle Parallel Server implementations.
Asynchronous I-O
Oracle configured with asynchronous I/O has been found to work effectively only on raw devices across most flavors of UNIX. Asynchronous I/O on regular file systems is supported on some operating systems such as Solaris. Depending on your I/O system configuration, you may observe that Direct I/O or Quick I/O can offer comparable performance when using specialized file
systems such as Veritas (vxfs). You may also have the option of configuring the relevant Oracle instance parameters for multiple database writer support. But normally you either enable asynchronous I/O or multiple database writers, not both.

regards
Mobeen

[Hein van den Heuvel]

Wim> Sometimes I still dream about the days before RAC made everything more difficult.

Ha, it makes me dream of Alpha just continueing (with A |d|i|g|i|t|a|l| logo on the box :-), with Tru64 and a native Cluster File System, Single System images, transparant cluster management, transparant disk serving, transparent mutli-path.

Soon, but not soon enough to hold you breath for it, coming to an hpux (11.31) system near you! (or 11.33, whatever). In our (Nashua, NH) labs today.

Grins,
Hein.

[Todd McDaniel_1]

NO points here...

I just rememebered a few more Pros for mounted oracle FS...

1) BCV Snapshots for Cold backups and Point-in-Time transaction reporting...
2) RMAN backups


I never liked RAW even when there was no other option, so I may be a bit jaded against raw devices for Oracle.