Re: lacing redo logs on Raw Devices instea dof cooked File Systes,

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Sybrand Bakker wrote:

> On 28 Sep 2004 14:33:30 -0700, premmehrotra_at_hotmail.com (Prem K > Mehrotra) wrote:

>>Sybrand Bakker <gooiditweg_at_sybrandb.verwijderdit.demon.nl> wrote in message
news:<oc8jl01s5qlverodvo6r1okege07uepeb1_at_4ax.com>...
>>> On 28 Sep 2004 08:12:57 -0700, premmehrotra_at_hotmail.com (Prem K
>>> Mehrotra) wrote:
>>>
>>> >I will be upgrading a database from Oracle8i to Oracle9i on HP UNIX.
>>> >Application tuning has already been done within the constraints that
>>> >it is an application bought from another company. It is single
>>> >instance database (i.e., no RAC). We will also be recreating Oracle9i
>>> >database and doing export/import from old to new and then applying
>>> >application level schema changes.
>>> >
>>> >Our application/database is clearly disk bound. We are using SAN. All
>>> >our file systems are cooked.
>>> >
>>> >I have read discussions on raw vs cooked on Oracle web sites as well
>>> >as in this forum. I am looking into moving only redo logs from cooked
>>> >file system to raw devices. Every time, I read about raw it clearly
>>> >bypasses UNIX buffer so should have some performance improvements. We
>>> >have 3 redo logs of 10K size. On the average every 3 minute a redo log
>>> >switch is made.
>>> >
>>> >I would think that there will be some performance improvement in gong
>>> >to raw devices. Since our database configuration for redo logs is
>>> >fixed (i.e., we do not expect to increase size of redo logs or number
>>> >of redo logs), once we set raw devices for redo logs, we are done.
>>> >Even if I get 5 to 10 performance improvement, I will prefer to use
>>> >raw devices.
>>> >
>>> >Does any one see any problem in using raw devices for redo logs only?
>>> >
>>> >Thanks a lot,
>>> >
>>> >Prem
>>>
>>> The performance improvement is more likely with setting a proper redo
>>> log file size. 10k is just clearly too small nowadays and you are
>>> switching too often. Oracle recommends an interval of 15 minutes
>>> between switches.
>>> Increasing the size of the online redo logs is almost one of the first
>>> things I do, when we take over a database from a third party.
>>> My *minimum* redo logs are 5M.
>>> I would first create proper online redo logs and then consider putting
>>> them on raw.
>>
>>Sorry, I had made a mistake, my redo log sizes are 10M and not 10K, so
>>I stll want to know whether using raw devices will be beneficial.
>>
>>Thanks,
>>Prem

> If you have switches every 3 minutes you should resize your redo logs. > PERIOD. > --
> Sybrand Bakker, Senior Oracle DBA

I agree with Sybrand. If you are switch every 3 minutes on average your redo logs are too small to begin with. There will probably be a performance benefit to switching to raw partitions over file systems but the benefit will likely be small. The reduction in redo log switches and associated work will likely exceed the benefit gained by switching the files to raw.

HTH -- Mark D Powell --

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