3 Replies Latest reply: Mar 4, 2013 1:55 PM by Levi Pereira RSS

    is it possible to create a raw device on a logical volume?

    872581
      Hi, all.

      The db is 11.2.0.3 on a linux machine.

      Is it possible to create a raw device on a logical volume WITHOUT cluster service from os vendor such as HACMP(AIX), Service Guard(HP)?
      The following is os information.
      
      [aa@mm01(abc):/home/abc] uname -a
      Linux aa 2.6.18-194.el5 #1 SMP Mon Mar 29 22:10:29 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux
      [aa@mm01(abc):/home/abc] 
      Thanks in advance.
      Best Regards.
        • 1. Re: is it possible to create a raw device on a logical volume?
          asahide
          Hi,

          Such command.
          # /usr/bin/raw  /dev/raw/raw1     /dev/Volume00/LogVol01
          This link will help you. (It does not matter whether the cluster..)
          <<http://www.dba-oracle.com/real_application_clusters_rac_grid/raw_devices_linux.html>>

          Regards,
          • 2. Re: is it possible to create a raw device on a logical volume?
            Catch-22
            The Linux kernel has traditionally not provided a raw interface, for a number of reasons. The use of raw device has been depreciated since RHEL 5 or kernel 2.6 and applications should use o_direct instead.

            Raw I/O is not always a performance boost since raw I/O operations are usually synchronous, meaning the write system call cannot return until the operation is complete. See the following link:
            support rawdevices by linux oracle.

            There is no need to create raw devices for Oracle 10.2.0.2 or later. The filesystemio_options parameter specifies how Oracle will perform disk I/O. DIRECTIO= Direct I/O, ASYNCH=Asynchronous I/O and SETALL=both.
            • 3. Re: is it possible to create a raw device on a logical volume?
              Levi Pereira
              Note:
              LVM configurations are not recommended by Oracle because they create a duplication of functionality. Oracle also does not recommended using LVMs for mirroring because ASM already provides mirroring.

              When using ASM avoid using a LVM because an LVM would be redundant. However, thereare situations where certain multipathing or third party cluster solutions require an LVM. In these situations, use the LVM to represent a single LUN without striping or mirroring to minimize the performance impact.

              Regards,
              Levi Pereira