IBM General Parallel File System (GPFS) and Oracle RAC

Oracle

2 comments to IBM General Parallel File System (GPFS) and Oracle RAC

• admin

  August 31, 2010 at 11:16 PM · Reply

  Direct I/O (DIO) and Concurrent I/O (CIO) on AIX 5L
  PURPOSE
  ——-
  To discuss the use of Direct I/O (DIO) and Concurrent I/O (CIO) on AIX 5L

  SCOPE & APPLICATION
  ——————-
  System Administrators managing AIX 5L that has Oracle RDBMS on top.

  DIRECT I/O (DIO) AND CONCURRENT I/O (CIO) on AIX
  ————————————————
  If you use a Journaled File System, it is easier to manage and maintain database
  files than it is if you use raw devices. In prior versions of AIX, file systems
  used to support only buffered read and write and added extra contention due to
  undesirable inode locking. These two issues are solved by JFS2′s Concurrent I/O
  and GPFS’ Direct I/O, allowing file systems to be used in place of raw devices
  even when optimal performance is required.

  AIX 5L includes Direct I/O support on JFS, JFS2 and GPFS. In addition, AIX 5L
  version 5.2 and later includes Concurrent I/O support. Direct I/O and Concurrent
  I/O support allows database files to exist on file systems while bypassing the
  operating system buffer cache and removing inode locking operations that are
  redundant with functionality provided by Oracle Database 9i. Where possible,
  Oracle recommends isolating Oracle data files on their own dedicated file
  system(s) on which the Concurrent I/O or Direct I/O option is enabled.

  The following table lists file systems available on AIX and the recommended
  setting:

  File System Option Description
  ———– —— ———–
  JFS dio Concurrent I/O is not available on JFS.
  Direct I/O (dio) is available, but performance
  is degraded compared to JFS2 with Concurrent I/O.

  JFS large file none Oracle does not recommend using JFS big file for
  Oracle Database because it’s 128 KB alignment
  constraint prevents you from using Direct I/O.

  JFS2 cio Concurrent I/O (cio) is a better setting than
  Direct I/O (dio) on JFS2 because it has support
  for multiple concurrent readers/multiple
  concurrent writers on the same file.

  GPFS – Oracle Database 9i release 2 and later silently
  enables Direct I/O on GPFS for optimum
  performance. GPFS already supports multiple
  reader/multiple writers/multiple nodes.
  Therefore, Direct I/O and Concurrent I/O are the
  same thing on GPFS.

  If GPFS is used, the same file system can be used for all purposes including
  $ORACLE_HOME, datafiles, logs. A large GPFS block size (typically at least 512KB)
  should be used for optimal performance. GPFS is designed for scalability and there
  is no requirement to create multiple GPFS file systems as long as the amount of
  data fits in a single GPFS file system.

  If placing the Oracle Database’s logs on a JFS2 filesystem, the optimal configuration
  is to create the file system with option “agblksize=512″ and to mount it with option
  “cio”. This delivers logging performance similar, within a few percents, to the
  performance of a raw device.

  In Oracle Database 9i, Direct I/O and/or Concurrent I/O can only be enabled at
  filesystem level on JFS/JFS2 and therefore $ORACLE_HOME and datafiles have to be
  placed in separate filesystems for optimal performance: $ORACLE_HOME would reside on
  a file system mounted with default options, whereas datafiles and logs would reside
  on file systems mounted with the “dio” or “cio” option.

  Having on ORACLE_HOME on a filesystem mounted with “cio” option is not supported.
  Such a configuration will cause, installation, relinking and other unexpected
  problems.

  RELATED DOCUMENTS
  —————–
  Note 232935.1 How to Enable DIRECT IO Support within Oracle and AIX with JFS2
  Filesystem
  Note 302806.1 IBM General Parallel File System (GPFS) and Oracle RAC on AIX 5L and
  IBM eServer pSeries
  Note 282036.1 Minimum Software Versions and Patches Required to Support Oracle
  Products on IBM pSeries

• admin

  August 31, 2010 at 11:17 PM · Reply

  How to Enable DIRECT IO Support within Oracle and AIX with JFS2 Filesystem
  PURPOSE
  ——-

  This article will assist you to configure the DIRECT IO Support within Oracle
  and AIX with JFS2 Filesystem

  SCOPE & APPLICATION
  ——————-

  This is intended for AIX system administrators and DBAs with sysadmin skills on
  AIX

  How to Enable DIRECT IO Support within Oracle and AIX with JFS2 Filesystem
  ————————————————————————–

  In AIX 5L (Version 5.2.0.10), also known as maintenance level 01, you either
  mount the corresponding file system with the

  mount -o dio

  option or you can use the ‘O_DIRECT’ flag in the file open() system call.

  This works for both JFS and JFS2 filesystems. A filesystem mounted with the
  “dio” option will have all I/O treated as Direct I/O as long as the alignment
  requirements are met. The I/O should be aligned to page (4K byte) boundaries and
  in multiples of the page size. If the I/O doesn’t meet those requirements, then
  the I/O will go through kernel buffers and the buffers will be flushed after
  the I/O completes.

  Oracle on AIX is a direct I/O capable application which writes according to the
  4K alignment.

  The setting of disk_asynch_io parameter and the number of dbwr_io_slaves or
  db_writer_processes depends the size of the buffer cache and whether a single
  dbwr can keep up with the I/O demands. The settings are not ‘necessarily’
  related to direct I/O.

  Note:
  —–

  IBM does not support Direct I/O on JFS2 filesystems in 9i.

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