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Re: RAID 5 7+1 with oracle

From: Frits Hoogland <frits.hoogland_at_gmail.com>
Date: Fri, 5 Oct 2007 10:30:38 +0200
Message-ID: <fbb8fbcd0710050130q320bdb1ahe96d54c48f209407@mail.gmail.com>


It's good to stick to the facts as close as possible.

At the end of the day the difference between writing in RAID 10 and 5 is:

RAID10: 1 write is done on two places, which can be done in parallel. RAID5: 1 write is resulting in 4 IO's
(If a block of data on a RAID5 disk is updated, then all the unchanged data blocks from the RAID stripe have to be read back from the disks, then new parity calculated before the new data block and new parity block can be written out. This means that a RAID5 write operation requires 4 IOs.)

If you think the BAARF stuff is outdated (which probably is true), please mind the principles still apply.

For quite some time we've got the centralised storage. Sadly, the discussion is still the same (centralised storage uses techniques for disk redundancy which is still RAID).

Centralised storage works happily as long as you do not overload any of the components inside it.
(CPU, cache, disk controllers, disks, disk channels, memory channels) In case someone wonders: this is not uncommon.

frits

On 10/5/07, Greg Rahn <greg_at_structureddata.org> wrote:
>
> In order to avoid a religious war I'll just offer this:
>
> Look at:
> http://h71028.www7.hp.com/ERC/downloads/4AA0-7923ENW.pdf
>
> This document shows that RAID5 (7D+1P : page 10 right graph) is far
> better than RAID 1(2D+2D : page 9 left graph) both on read and write
> operation.
>
> From a price/performance perspective RAID5 beats RAID10 by quite a
> bit. Also, today's high end storage arrays have a very fast asic
> chips and large cache that make the two very competitive.
>
> Personally I've done numerous muti-terabyte (20TB-75TB) DW benchmarks
> using RAID5 and have had no complaints on the performance.
>
> Depending on how dirty you want your hands to get... pick up Oracle
> Orion tool [http://www.oracle.com/technology/software/tech/orion] and
> do some read & write tests.
>
> You might want to use some discretion with the BAARF stuff. I think
> much of it is outdated. Storage technology has probably changed quite
> a bit since 2000. CPUs certainly have.
>
> Another resource is:
> http://www.storageperformance.org/results/benchmark_results_spc2
>
> Many of the arrays have been tested at both RAID5 and mirroring.
> Check the reports for the details.
>
> On 10/4/07, ryan_gaffuri_at_comcast.net <ryan_gaffuri_at_comcast.net> wrote:
> >I have read the BAARF articles about RAID and write intensive Oracle
> >databases. Are any of these problems mitigated with RAID 5 7+1. I did
> some >googling, but the 7+1 part is not really clear. Has anyone
> worked with >this?
>
> --
> Regards,
>
> Greg Rahn
> http://structureddata.org
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

--
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Received on Fri Oct 05 2007 - 03:30:38 CDT

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