Re: ASM Question - Best Practice

On Wed, 04 Jun 2008 15:59:00 -0700, DA Morgan wrote:

> I think you are misunderstanding Mladen's comment. Of course the SA's
> have to label the disks and present them to the O/S.

Yes, that is still true.

> But thereafter the
> DBA can manage the available space without having to bring in people
> that, all too often, have no interest in understanding Oracle and the
> needs of the DBA team.

That is right. In addition to that, when using raw devices without the ASM layer, you can have device assigned to a single tablespace only. No reuse. If you have a big TS which is, for some reason no longer required, (this happened to me when the company that I am working for changed the rules of archiving and decided to keep old data on DVDs, rather then in the database) you cannot re-size it if you are using raw devices. You can either drop it or keep it. With ASM, you can re-size files and have other tablespaces reuse that same space, without the intervention of a system administrator.

>
> My opinion is that for almost everything Oracle ... ASM is the way to
> go.

I don't necessarily agree with that. File systems are still more versatile then ASM. If you can get a cluster file system with support for both coordinated cache and direct I/O (like VxFS/CFS or HP Polyserve) it will provide equal performance and easier administration. Of course, it costs money. I must confess that I experimented with GFS and have created a RAC with Oracle CRS, voting and quorum on raw devices and data files on GFS. Performance was rather good, completely comparable to ASM. My only problem is that I don't really trust GFS. It's still too new and if there is a problem, I can get myself in a really big mess. For instance, OCFS is known to have had corruption problems. I want to have support behind my cluster file system, it's not yet a common technology.

Matt Zito of GridApp in NYC has been experimenting with GFS for a lot longer then me and he might be of a different opinion. Matt is, besides Oracle's Kevin Closson and K. Gopalakrishnan, the foremost living authority for all things RAC. He had probably forgotten more about RAC than I've ever known. If that was an option, I'd consult GridApp for planning RAC deployments.

Also, modern NFS4 NAS devices are a good option. NetApp is the 1st that comes to mind. I didn't actually try it, but I saw a few demos done by NetApp. It was impressive. Also, NetApp has a very impressive snapshot backup technology. Kevin Closson had a word or two about NFS and RAC on his blog.

ASM is a good option but I am skeptical toward silver bullet talk, like "the best option for everything Oracle". ASM doesn't have a FS interface and that's its most severe limitation. If one needs a file system, ASM is not a solution.

-- 
Mladen Gogala
http://mgogala.freehostia.com