Re: DBA Experiences with Oracle and RAID 0+1

Diego,

I agree with you 100% and didn't express myself correctly in my email. The more spindles the better. What I meant to say was that you must never buy disks by taking your total needed amount of space and divide by the number of big disks you can get hold on :). It's the number of IO's required by the disk system that matters, not the size...

Thanks for making this clear to everyone.

Mogens
Diego Cutrone wrote:

  Mogens: Just let me disagree with you at only one point. According to myexperience, I think that the size of the disks in an array does mattersometimes. It's not the same to have 24 9GB disks that to have only 3 of73GB. You have 24 spindles againts 3, the first option (in a well configuredsystem of course) will give you better performance in enviroments where youhave a lot of concurrency and many users. However I think that what I've written above might not be correct (maybe it should be tested) if the 73GB outstands for a long way the 9GB disksin terms of seek time and transfer rate. Take a look at an extract of Gaja's paper "Implementing RAID on Oracle":"5) Procure the smallest drive money can buy, keeping in mind scalability,limits of the hostmachine, the disk array and growth projections for the database. This is atough one thesedays, with 18 GB drives considered as small drives.< br>6) Bigger and faster drives are not always better than smaller slowerdrives, as the seek timesfor larger and faster drives with larger form factors, may be more thantheir smaller andslower counterparts. This is not that big of an issue, if your drivessupport a built-in trackbuffer cache for storing an entire track's worth of data from readrequest(s)."HTHGreetingDiego Cutrone----- Original Message -----To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>Sent: Tuesday, January 15, 2002 10:25 PM   

    Jon,It's one of those "how many bags will I need in the supermarket?"questions - it depends.Consider:- RAID 1+0 is much better than 0+1.- Three disks is not much w.r.t. IO capability. If you have threeconcurrent users you'll be OK :)- Size doesn't matter (who cares if it's 10, 36 or 73 Gig disks? It'sthe IO capabilitity that counts)- I'm new to this list, so I don't know if this will work, but I'veattached a brilliant presentation by our old friend James Morle (checkout www.ScaleAbilities.com) regarding SAN, NAS and RAS (Random AcronymSeminar).- If you're only striping across three disks (is that really a SAN?)just SAME (Stripe And Mirror Everything). It might not be good, but it'ssimple.Jon Behnke wrote:     

      We are in the process of setting up a SAN using RAID 0+1 for our
      
      
      database.
      
        
          In our current environment, we are able to separate our tables, indexes,rollback segments, and archive logs on different disks.  On the SAN we
          
          
          would
          
            
              have six 73 gig disks on RAID 0+1 for a total of about 210 Gig of usablespace (3 disks worth of space).Some white papers that I have read suggest attempting to separate the
              
              
              data,
              
                
                  indexes, and rollback segments on separate RAID volumes, and others
                  
                  
                  simply
                  
                    
                      suggest that the performance boost of striping will supercede the
                      
                      
                      separation
                      
                        
                          of these items.Can anyone offer any comments or suggestions?Jon BehnkeApplications Development ManagerIndustrial Electric Wire & CablePhone (262) 957-1147  Fax (262) 957-1647jonb_at_iewc.com