Re: DASD Disk Layout Advice

From: joel garry <>
Date: Wed, 25 Nov 2009 10:08:45 -0800 (PST)
Message-ID: <>

On Nov 24, 7:18 pm, Pat <> wrote:
> For the last few years, I've largely been laying out Oracle storage on
> SAN's, rather than on DASD, so I'm feeling a bit out of practise with
> today's drives and drive arrays.
> To make a long story short, I've got a new Oracle server in a remote
> data center that I didn't order or configure; it comes like it comes.
> Its a 32G 8 core intel box with 8 300G 15k SAS drives in it and a
> decent raid controller. Database in question is somewhere between a
> data warehouse and OLTP e.g. its read heavy, but there's still a very
> significant amount of write activity.
> I've got a colleague who, wants to build out the box something like:
> Disk0 .. RedoA
> Disk1 .. RedoB
> Disks 2..3 RAID 1 OS and Index tablespace
> Disks 4..7 Raid 10 Data tablespace
> My instinct is that buildout "wastes" too many spindles and ends up
> starving the index and data volumes.
> The counterproposal is to just make one big raid group like:
> Disk 0..7 Raid 10
> What are folks doing these days with these bold 'old 300G disks? It
> seems supremely wasteful to use an entire 300G drive hold 20G worth of
> red.
> Any recommendations, advice, etc would be appreciated.

The essential problem is the difference in write characteristics for redo. Spreading everything among spindles is good, but the limiting characteristic will be whether the controller buffering will be saturated. If it saturates, performance will go downhill at unpredictable times, and fast. The redo is critical. "A decent controller," does that mean one path?

It is difficult to come up with a showing that separating out indices and data is good for performance. Some people thought that in the past, but it is simply an artifact of splitting I/O among drives. A much better split may come from seeing which tablespaces use the most I/O. For my OLTP type systems (aside from redo), I see most I/O going towards (drum roll, please)... undo. YMMV. The important point is to test the configurations with your load.

Will someone please tell the manufacturers that size of disk is less important than number of spindles for us db types?


-- is bogus.
Received on Wed Nov 25 2009 - 12:08:45 CST

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