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Which file system(OCFS) or RAW device vs ASM to choose for shared disk in RAC

Depending on manageability and performance trade off this is a very important question: My view based on my practical experience is below.
  • OCFS is the best for manageability as you have transparent and visible file system like any other file system NTFS or ext3/4 etc on Linux. However OCFS has bugs and under very heavy I/O load its performance deteriorates. Another reason to go for OCFS is you can have shared Oracle Home so patching Oracle home is quicker. In my first experience of Oracle RAC which was 9iR2 RAC on Production on Windows  2K we had OCFS file system and there were few bugs which due OCFSTOOL would give false warnings. And in one case OCFS was not freeing up space after deleting files on file system. Later on I used OCFS 2 on Linux for test purposes and I did not get same issues but it was very limited test. Oracle 11.2.0.1 had issue in directly accessing OCFS file system so it has to be mappped by NFS. OCFS has matured a lot but Oracle seems is not keen to promote it now.
  • I used pure RAW devices on single instance database in test environment and its performance was slightly better than on file system but it wa diifficult to manage. Once, in early of my career I got opportunity to recover a Oracle 8i Production OPS (previous name for RAC) Database  and only option to used shared device was raw only. It was my first attempt of any recovery on RAC database and I was not practically familiar with RAW devices by that time but Oracle documentation was good enough for me to partition new replaced disk and tell how to copy on raw devices the files from backup  

  • ASM(using RAW or ASMLIB or  UDEV) :  ASM can be said to lie between mid of the raw file system and file system. Performance benefit slightly reuced from RAW file system,better than file system,  but better manageability as advantage in its comparison. ASM can be used on top of raw devices services or by using ASMLIB(2 rpms provided by Oracle corp and  1 from OS kernel vendor say RHEL). From 11gR2 ASM using RAW devices is supported only with the systems upgraded from 11g. My preferred way from performance point of view is to use ASM is ASM with UDEV rule as it does not involve extra layer of ASMLIB kernel on top of kernel.Only advantage of ASMLIB is see is easy to maintain shared disks. It takes some time to be familiar with UDEV rule and it is not uniform across all shared disks type but I do not think you often add/remove disks. You will be surprised to know that even though Oracle recommends using ASMLIB for better performance but Oracle itself is not using it in Oracle RAC using Oracle VM templates. If you are using RHEL 6 and not OEL 6 then there is compelling reason that you must subscribe to RHLN to get ASL kernel driver else your only option to use is to use UDEV rule

After recovering Oracle 8i OPS for STP Noida [ night long task on voluntarily SOS call by my friend, so took no money :)  ] - year 2006



See my other post with label ASM for configuring UDEV.

tag: OCFS vs ASM, ASMLIV vs UDEV





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