Oracle 10g Automatic Storage Management

1
Oracle 10g Automatic Storage Management

• Overview of ASM as a Storage Option for Oracle
  10g

2
Objectives

• At the end of this module the student will
  understand the following tasks and concepts.
• Understand the role of ASM
• Understand ASM components
• Understand how ASM handles disk redundancy
• Understand ASM Disk Groups
• Understand ASM Directories and Files
• Understand the uses of the ASMCMD command
• Understand how OEM interfaces with ASM

3
Automatic Storage Management

• ASM is a storage management system for Oracle
  data
• ASM is designed to simplify DBA storage tasks
• Simply assign disks and walk away no data
  layout decisions
• Allows Oracle to manage thousands of files
  automatically
• Organizes available disks into disk groups

4
ASM and Oracle Managed Files

• ASM extends the power of Oracle Managed Files
• Creates and manages files automatically
• Understands different Oracle file types
• Offers built-in data mirroring and striping
  capabilities
• Automatically balances I/O load across disk
  group(s)
• Functionally like an LVM (Logical Volume Manager)

5
ASM Database

• When ASM is enabled, Oracle automatically creates
  a small database for storing ASM-related
  meta-data
• The default database name is ASM
• The default RAC instances are ASMn, where n is
  the node number
• The ASM database may be managed with srvctl
  commands
• Normally auto-managed by Oracle

6
ASM Components

• Disk Groups
• Oracle may provide disk mirroring (optional)
• Oracle will stripe files across all available
  disks
• Using ASM striping across a group of hardware
  striped LUNs can be beneficial to performance
• Disks assigned to ASM Disk groups become ASM
  Disks
• Files written on ASM disks become ASM files
• Files are named with an Oracle-defined format
• File name aliases may be defined for convenience
• A hierarchical directory structure may be defined
  for file aliases

7
ASM Components

• Templates may be used to associate file
  attributes such as redundancy and striping with
  ASM files
• ASM is implemented through an ASM instance that
  runs as a service on each node

8
ASM Disk Group Redundancy

• ASM Disk Groups may be defined with different
  levels of redundancy
• NORMAL redundancy indicates that Oracle will
  create a software mirror for each disk
• HIGH redundancy indicates that Oracle will create
  two mirror disks per data disk
• Disk mirrors may be segregated into different
  locations by designating Failure Groups
• EXTERNAL redundancy indicates that Oracle will
  not create any software mirrors. Hardware
  mirrors (if any) will be used instead
• External redundancy is recommended for any system
  with a highly available storage array

9
ASM Performance Tips

• ASM performance is sensitive to the number of
  disk spindles utilized
• Just like traditional storage, the number of
  IOs/second that can be sustained is directly
  proportional to the number of disks in the disk
  group
• Always use External Redundancy if you are using
  RAID-capable storage hardware
• Multiple RAID 1 disks can be utilized in a Disk
  Group
• ASM will provide the disk striping
• Another option is to use multiple four disk RAID
  10 groups as the building block for ASM Disk
  Groups
• ASM will stripe on top of the hardware stripe,
  creating a stripe plaid, very desirable for
  OLTP and random I/O performance

10
Creating ASM Disk Groups

• ASM disk groups may be created as part of the
  installation process
• Raw device files may be used though their file
  name aliases
• As an alternative to raw files, ASMLIB may be
  used to stamp raw device files
• Creates a name alias for the raw device files
• The CREATE DISKGROUP SQL statement may be used
  to create disk groups
• CREATE DISKGROUP dgroup_01 EXTERNAL REDUNDANCY
  DISK C\ASM'
• The disk group created in this example will be
  referred to as dgroup_01

11
ASM File Creation

• ASM files will be created automatically by Oracle
  when a new object is created
• ALTER SYSTEM SET DB_CREATE_FILE_DEST
  'dgroup_01'
• CREATE TABLESPACE mytspace1
• Note ASM files are only visible to Oracle
  through SQL, ASMCMD, Grid Control, or OEM
• Not visible as an OS level file looks like a
  raw device to the OS

12
ASM File Formats

• ASM files have the following format
• group/dbname/file_type/file_type_tag.file.incarna
  tion
• Where
• group is the disk group name
• dbname is the DB_UNIQUE_NAME of the database
• file_type is the Oracle file type
• tag is a descriptor appropriate to the file type
• file.incarnation is the file/incarnation pair,
  used to ensure uniqueness
• An example of a fully qualified ASM filename is
• dgroup_01/oradb/controlfile/CF.248.1

13
Creating ASM Directories

• Before creating an alias for an ASM file, you
  must first create a directory hierarchy to
  contain the file
• ALTER DISKGROUP dgroup_01 ADD DIRECTORY
  'dgroup_01/newdir'

14
ASM File Aliases

• An alias may be created in SQL for an ASM file
  name
• ALTER DISKGROUP dgroup_01 ADD ALIAS
  'dgroup_011/newdir/control_2.dbf' FOR
  'dgroup_01/oradb/controlfile/CF.248.2'
• Oracle Enterprise Manager may be used to assign
  file aliases
• An SQL statement is still required to create the
  directory (as of Oracle 10g R1)

15
Creating a Tablespace with ASM

• Creating a Tablespace in ASM Example 1
• Let Automatic Storage Management create and
  manage the tablespace datafile for you
• Assume the following initialization parameter
  setting
• DB_CREATE_FILE_DEST 'dgroup2'
• The following statement creates the tablespace
  and its datafile
• CREATE TABLESPACE tspace2

16
Creating a Tablespace with ASM

• Creating a Tablespace in ASM Example 2
• The following statements create a tablespace that
  uses a user defined template to specify the
  redundancy and striping attributes of the
  datafile
• SQLgt ALTER SYSTEM SET DB_CREATE_FILE_DEST
  'dgroup1(my_template)'
• SQLgt CREATE TABLESPACE tspace3

17
Creating a Tablespace with ASM

• Creating a Tablespace in ASM Example 3
• The following statement creates an undo
  tablespace with a datafile that has an alias
  name, and with attributes that are set by the
  user defined template my_undo_template (not
  Oracle Managed Files).
• CREATE UNDO TABLESPACE myundo DATAFILE
  'dgroup3(my_undo_template)/myfiles/my_undo_ts'
  SIZE 200M

18
ASMCMD

• ASMCMD is a command-line utility for viewing and
  manipulating files and directories within ASM
  disk groups.
• Can be used in interactive mode
• Commands can be placed in OS scripts
• Available with 10g R2
• ASMCMD can be used to
• List the contents of disk groups
• Perform searches
• Create and remove directories and aliases
• Display space utilization
• And more.

19
ASMCMD Syntax

• Command Description
• cd Changes the current directory to the
  specified directory.
• du Displays the total disk space occupied by ASM
  files in the specified ASM directory and all
  its subdirectories, recursively.
• exit Exits ASMCMD.
• find Lists the paths of all occurrences of the
  specified name (with wildcards) under the
  specified directory.
• help Displays the syntax and description of
  ASMCMD commands.
• ls Lists the contents of an ASM directory, the
  attributes of the specified file, or the names
  and attributes of all disk groups.
• lsct Lists information about current ASM
  clients.
• lsdg Lists all disk groups and their attributes.
• mkalias Creates an alias for a system-generated
  filename.
• mkdir Creates ASM directories.
• pwd Displays the path of the current ASM
  directory.
• rm Deletes the specified ASM files or
  directories.
• rmalias Deletes the specified alias, retaining
  the file that the alias points to.

20
ASMCMD Example

• In the following example, the rm command operates
  on the file undotbs1.272.557429239, which in this
  case is a relative path.
• ASMCMD prepends the current directory to the
  command argument to obtain the absolute path to
  the file
• ASMCMD gt cd dgroup1
• ASMCMD DGROUP1 gt cd sample/datafile
• ASMCMD DGROUP1/SAMPLE/DATAFILE gt ls
• EXAMPLE.269.555342243
• SYSAUX.257.555341961
• SYSTEM.256.555341961
• UNDOTBS1.258.555341963
• UNDOTBS1.272.557429239
• USERS.259.555341963
• ASMCMD DGROUP1/SAMPLE/DATAFILE gt rm
  undotbs1.272.557429239

21
OEM (Grid Control) ASM Home Page

• In Grid Control or Database Control (OEM) you can
  log into an ASM instance target (usually ASMn)
• Check overall Disk Group health
• Specific tabs for
• Performance
• Administration
• Maintenance

22
OEM (Grid Control) ASM Performance Page

• Performance Graphs for Disk Group metrics
• Disk Group I/O response Time
• Disk Group I/O Operations
• Disk Group I/O Throughput

23
OEM (Grid Control) ASM Administration Page

• Provides administrative access to disk groups
• Mount Disk Groups
• Dismount Disk Groups
• Create Disk Groups
• Drill down to more detail

24
OEM (Grid Control) ASM Configuration Page

• Configure parameters for Disk Groups
• Data Discovery Path path for discovering Disk
  Groups
• Auto Mount Disk Groups list of Disk Groups to
  mount automatically at startup
• Rebalance Power affects speed of Disk Group
  rebalancing. High numbers are faster, with more
  I/O overhead (1-11)

25
Review

• Should you use normal redundancy for a RAC system
  on a SAN?
• What ASM component associates redundancy and file
  striping attributes with a file type?
• Do you have to create a file name for each new
  Oracle object?
• List the format of a fully qualified ASM file
• Give an example of an ASCMD command.

26
Summary

• ASM provides an easy-to-administer option for
  allocating storage
• ASM extends the concept of Oracle Managed Files
• ASM can provide both disk striping and disk
  redundancy
• ASM components include Disk Groups, ASM Disks,
  Templates and ASM instances
• ASM Directories, Files and File Aliases may be
  optionally created
• ASMCMD may be used to simulate a traditional file
  system command line interface
• Grid Control (OEM) provides several useful ASm
  oriented screens