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

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