Re: DASD Disk Layout Advice

From: Vladimir M. Zakharychev <>
Date: Wed, 25 Nov 2009 09:01:24 -0800 (PST)
Message-ID: <>

On Nov 25, 6:18 am, 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.

You might want to take a look at ORION here:, and setup a few experiments with different disk layouts and workloads to have an idea of what to expect in different configurations and what would work best for your particular implementation.

In theory, dedicating a couple of spindles (or better yet, SSDs) purely for redo mirrors would minimize redo log sync waits, which could be beneficial for OLTP, but with today's high-performance RAID controllers with large built-in battery-backed write caches this is probably an overkill and does not worth the disk space wasted unless you really need top performance (in which case you'd probably look towards Exadata v2 anyway.) Though you could procure a couple of smaller disks for this (in 80-100GB range,) their price difference is really negligible and you will still waste most of their capacity.

And then there's ASM, which you can use to build a single disk group with external redundancy on top of your RAID10 volume and store everything there (and let Oracle handle different file types automagically.) ORION will help you test this approach as well as native ASM striping (that is, no hardware RAID, treat the array as JBOD and do redundancy and load balancing in Oracle software.)

And results of your experiments might constitute for a nice blog entry. ;)


   Vladimir M. Zakharychev
   N-Networks, makers of Dynamic PSP(tm) Received on Wed Nov 25 2009 - 11:01:24 CST

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