RE: RAC storage newbee question

From: Mark W. Farnham <mwf_at_rsiz.com>
Date: Mon, 26 May 2014 13:37:15 -0400
Message-ID: <00a801cf7909$236a9d90$6a3fd8b0$_at_rsiz.com>

It is hard to beat external redundancy on hardware enabled raid 1, duplex or triplex. Raid 0 is a real puzzler, because when you play them on ASM and string them together you probably end up slicing across each disk to have small enough chunks to deal with. ASM will stripe across the disks you give it. The best thing to give ASM is a single platter (or two or three platters that operate duplex or triplex as the same unitary piece of acreage if you go external.)  

The complex cross hatch utilization pattern that may develop from handing ASM disks that are already striped is just that: complex. It is not clear whether you win or lose from mathematical modelling but there is potential for lots of extra seeking at the physical spindle level when you're drinking full 1MB or 4MB drinks. For little reads it is probably a wash, so my advice is to avoid the possible unfortunate i/o pattern.  

But this may vary with the precise disk farm configuration. Compared to software raid, ASM might do better.  

Is there no opportunity to spin up a test with your planned load?  

Probably the most important thing about handing pieces of storage to ASM from a pool is to make sure that the physical components underlying your pieces are not simultaneously also in usage by any other loads (especially loads that you cannot observe and control, which is frequently true if the storage is being provided from a pool.)  

mwf  

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Chris King
Sent: Monday, May 26, 2014 12:40 PM
To: oracle-l_at_freelists.org
Subject: RAC storage newbee question  

Thanks in advance for your feedback on this question.  

We built RAC in a lab using VMs and now are planning to build on metal. We're using ASM for disk storage management, so I requested raw disk.  

I'm told by the storage admin that he can not provide raw disk. Although he could provide raid 0.  

So my question is:

If I ask the storage manager to provide disk that is already raid 0+1, and then I create ASM disk groups using the "external" option. Is this approach any better/worse than providing ASM raw disk to manage?  

(I would use the external option so that I don't end up striping and mirroring disk that is already striped and mirrored.)  

Or would it be better to have him provide all the disks as raid0, and have ASM handle all the redundancy?            

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Received on Mon May 26 2014 - 19:37:15 CEST