RAID5 or RAID50 for database?

Aaron dell at microchp.org
Fri May 23 20:33:27 CDT 2008


I have seen some of the responses thus far and wished to chime in with 
my experience.  The old discussions of which raid offers the best 
results can all be thrown out the window.  You have to first understand 
what you are using it for and what you will be doing 95% of the time.  
For example, a read-intensive database can actually get better results 
using raid-5 over raid-10 with certain raid controllers, whereas a write 
intensive database can get better results with raid-10.  A storage 
company would never agree with this because it means selling less 
disks.  ;-)  Such things depend on the hardware, the database 
configuration and of course the use of the database.  This also depends 
on how your OS and database make use of the storage. (See directIO, AIO 
or Asynchronous IO which Oracle did not use by default on linux)

I would ignore any responses (including mine) that you get on this list 
and instead look at the characteristics of your database.  With modern 
storage and operating systems; the rules have somewhat changed, so it is 
best to run your own performance tests.  There are numerous free tools 
to see what works best on your hardware, such as bonnie++.  You and/or 
your DBA should be able to tell which volumes would benefit the 
most/least from read or write performance.  There are also boot options 
that change the IO scheduling characteristics as well.  Google for 
"elevator=deadline database" and you will run across some of the Oracle 
and IBM documentation on this.  Just keep in mind when reading Oracle 
documentation that most of it is contradicting to itself and not checked 
for accuracy.

Good luck with your database.  :-)


Regards,

Aaron


P.S. - While you can technically do RAID-50 on 4 disks, it requires 
splitting up the disks into partitions that would then be used as 
software-raid devices and would defeat the purpose.  Perhaps I also 
misunderstood the initial question.  ASCII bunny says no more coffee for 
me today and back to WoW.



Matt Lawrence wrote:
> mcclnx mcc wrote:
>   
>> we have DELL 6800 server with 12 internal disks in it. O.S. is CENTOS
>> 4.6 and SCSI control card is PERC 4e/di.
>>
>> We plan to configure 4 disks (5,8,9,10) as RAID5 or RAID50. This
>> logical volume will be use as file systems and store database backup
>> files.
>>
>> Can anyone tell me which one is better on performance?
>>     
> RAID50 with only 4 disks? Perhaps you should rethink that idea.
>
> -- Matt
>
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