3
Performing Pre-Installation Tasks

This chapter describes required pre-installation tasks. Specific topics discussed are:

• Raw Partition Overview

• Step 1: Create an Extended Partition

• Step 2: Create Logical Partitions In an Extended Partition

• Step 3: Unassign Drive Letters

Raw Partition Overview

Because no true distributed file system support exists on Windows NT, the mechanism Oracle uses to allow nodes running different instances to access shared disks is to bypass the NT file system by using raw partitions. The shared disks are then a collection of unformatted raw devices.

Raw Partition

A raw partition is a portion of a physical disk that is accessed at the lowest possible level. I/O to a raw partition offers approximately a 5% to 10% performance improvement over I/O to a partition with a file system on it.

A raw partition is created when an extended partition is created and logical partitions are assigned to it without applying any formatting. The Windows NT Disk Administrator application allows you to create an extended partition on a physical drive.

Extended Partition

An extended partition points to raw space on the disk that can be assigned multiple logical partitions for the database files. An extended partition avoids the four-partition limit by allowing you to define large numbers of logical partitions to accommodate applications using Oracle8 Enterprise Edition. Logical partitions can then be given symbolic link names to free up drive letters. We create an extended partition in this chapter and link the drive letters to symbolic link names in Chapter 5, "Configuring Oracle Parallel Server".

The Disk Administrator window in Figure 3-1, "Disk Administrator" shows four disks, two of the disks having an extended partition.

Figure 3-1 Disk Administrator

This disk....	Contains...
Disk 0	a primary partition
Disk 1	an extended partition with six logical partitions and 246 MB of free space
Disk 2	an extended partition with three logical partitions and 1146 MB of free space
Disk 3	an unformatted partition

Note: You can tell whether a partition is formatted or unformatted by the direction of the diagonal lines. A formatted partition's lines display from top left to the bottom (\\), and an uninitialized partition's lines display from top right to the bottom (//).

Disk Definition

Windows NT defines each disk drive found at startup with the following naming convention:

\Device\Harddiskm\Partitionn

where Harddiskm is the number of the physical drive, and Partitionn is a logical partition number, as shown in the Disk Administrator window (in Figure 3-1, "Disk Administrator"). Harddiskm starts at 0, and Partitionn starts at 1. Partition0 has a special meaning in that it has access to the whole disk. For example, the first logical partition (E:) on the second physical drive in Figure 3-1, "Disk Administrator" has the following entry:

\Device\Harddisk1\Partition1

The first logical partition on a system (normally the C drive) has the following entry:

\Device\Harddisk0\Partition1

Raw Partition Definition

Raw partitions are of two types:

• Physical Disk

• Logical Partition

  Note: Although you can use physical disks, Oracle Corporation recommends using logical partitions and creating symbolic links (as described in section "Step 2: Assign Symbolic Links to Each Logical Partition").

Physical Disk

A physical disk represents the entire disk. It points to \Device\Harddiskx\Partition0. Windows NT automatically creates a symbolic link name of \\.\PhysicalDrivex, where x is the number corresponding to your hard disk drive number in the Disk Administrator. The x matches the x in \Device\Harddiskx\Partition0.

\\.\PhysicalDrivex is automatically defined by Windows NT for every hard disk in the machine. For example, a machine with three hard disks will have the following names defined by Windows NT:

\\.\PhysicalDrive0

\\.\PhysicalDrive1

\\.\PhysicalDrive2

Internally, these names expand to:

\\.\PhysicalDrive0 = \Device\Harddisk0\Partition0

\\.\PhysicalDrive1 =\Device\Harddisk1\Partition0

\\.\PhysicalDrive2 =\Device\Harddisk2\Partition0

Partition0 is special in that it represents the entire physical disk regardless of any partitioning scheme on that disk. On all disks recognized by Windows NT, the Disk Administrator writes a signature on the first block of all disks. To avoid overwriting that block, Oracle skips the first block of a physical raw partition which is used for an Oracle data file.

Logical Partition

A logical partition is a partition created by the Disk Administrator that points to a drive other than \Device\Harddiskx\Partition0. Logical partitions are initially assigned names with drive letters (\\.\drive_letter:) and typically re-assigned symbolic link names (\\.\symbolic link name). For example, \\.\D: may be assigned a symbolic link name of \\.\OPS_SYS01. Regardless of whether a drive letter or symbolic link name is used, logical partitions are defined to represent a specific partition in a disk rather than the entire disk. Internally, these names may expand to:

\\.\D:= \Device\Harddisk2\Partition1

\\.\OPS_SYS01= \Device\Harddisk3\Partition2

Drive letters can be assigned to specific partitions using the Disk Administrator, while symbolic link names can be assigned using a utility such as DOSDEV.EXE, which is available with the Windows NT Resource Kit, or the SETLINKS utility (shipped with the Parallel Server Option).

Note: Oracle does not skip the first block of a logical raw partition used for an Oracle data file.

Physical Disk and Logical Partition Considerations

Please consider the following when deciding which raw partition to use:

• Physical disks are automatically defined by Windows NT to represent the entire disk, and should never be defined by the user.

• Logical partitions need to be defined by the user to represent a specific partition in a disk. These partitions should be logical partitions or drives contained in an extended partition. They should never be defined as Partition0.

• Using an entire disk (Partition 0) for an Oracle data file and using a partition which occupies the entire disk for an Oracle data file is not the same thing. Even when a partition occupies the entire disk, there is still a small space on the disk that is not part of the partition.

• If you are using an entire disk for an Oracle data file (Partition 0), use the pre-defined physical raw names which Windows NT provides.

• Use a logical partition if you are using a specific partition and it occupies the entire disk.

• If using a specific partition created with the Disk Administrator, define and use a symbolic link name rather than a logical partition number (even if it occupies the entire disk).

Frequently Asked Questions

Question: What is the impact if I have created logical partitions, but defined physical disk convention names for them. For example:

\\.\PhysicalDriveSYS01 = \Device\Harddisk2\Partition1

\\.\PhysicalDriveUSR01 =\Device\Harddisk3\Partition1

Answer: Oracle database will handle the data file using the physical disk convention, even though it really is a logical partition. This will not cause any data corruption or loss, as long as you continue using the physical disk naming conventions. Oracle Corporation recommends you convert to the logical partition at your earliest convenience. See "Compatibility Issues".

Question: What is the impact if I have created logical names representing Partition0. For example:

\\.\OPS_SYS01 = \Device\Harddisk1\Partition0

Answer: This will pose severe problems, as the Disk Administrator typically writes a signature into the first block of every disk, and consequently may overwrite a portion of the data file header.

This may also cause data loss. Never use Partition0 with the logical partition convention. See "Compatibility Issues" for information on rebuilding your Oracle database with the proper conventions.

Question: How do I transfer the contents of any raw partition to a standard file system for backup purposes?

Answer: Use the Oracle provided OCOPY to copy data to/from a raw partition for both physical and logical raw conventions. See "Compatibility Issues" for further information.

Compatibility Issues

The physical and logical partition conventions are not compatible with one another due to the extra block that is skipped for physical raw conventions. This also means you cannot simply do an OCOPY from a physical disk to a logical partition, as the contents of these partitions are incompatible.

To convert from a physical convention to a logical convention, you must:

1. Perform a full database export to a (local) file system.

2. Create logical partitions and define logical names for these partitions.

3. Re-create the database using the new logical partitions.

4. Perform the full database import to the newly created database.

If your database installation uses physical disk conventions with logical partitions, Oracle Corporation recommends converting to the logical partition conventions at your earliest convenience using the steps above.

Step 1: Create an Extended Partition

Only one extended partition can be created per disk. You can use the free space in the extended partition to create multiple logical partitions or use all or part of it when creating volume sets or other kinds of volumes for fault-tolerance purposes.

To create an extended partition:

1. Shut down all nodes except the primary node.

2. On the primary node, choose Start > Programs > Administrative Tools > Disk Administrator.

   The Disk Administrator window appears:

   
   

   Note the lines display diagonally from top right to the bottom left, indicating unpartitioned devices.

Select an area of free space in an extended partition on a disk that is on the shared disk subsystem by clicking the mouse.

Oracle recommends you use the entire disk.

Choose Create Extended... from the Partition menu.

The Disk Administrator displays the minimum and maximum sizes for the extended partition:

Use the default maximum size, then click OK.

Note: Changes you have made are not saved until you choose Commit Changes Now Commit Changes Now from the Partition menu or quit the Disk Administrator.

The extended partition is created.

Note the lines now display diagonally from top left to bottom right, indicating the partition is an extended partition.

Step 2: Create Logical Partitions In an Extended Partition

After an extended drive is created, you must assign logical partitions to it. Logical partitions are assigned letters of the alphabet.

To create logical partitions in an extended partition:

1. On the primary node, select an area of free space in an extended partition by clicking the mouse on it.

2. Choose Create from the Partition menu.

   The Disk Administrator window displays the minimum and maximum sizes for the logical partition:

   
   
3. Enter the size of the logical partition, then click OK.

   The size is dependent on how large you want your log files and data files to be. Add 2MB to this size for overhead. If you plan on using the default database OPS.SQL creation script (to be used later) located in ORACLE_HOME\OPS to create your database later, 300 MB is more than enough.

   Additional Information: See "Step 7: Create an Oracle Parallel Server Database" for more information about OPS.SQL.

4. Repeat Steps 1-3 until you have nine logical partitions.

   Attention: A two-node cluster requires 9 drives, and each additional node requires 2 additional drives to accommodate log files.

5. Choose Commit Changes Now from the Partition menu.

   A confirmation dialog appears, informing you changes have been made to the disk.

6. Click Yes to acknowledge the message.

   A dialog box appears, informing you the disks have been updated successfully.

7. Click OK.

8. Choose Close from the Partition menu.

9. Reboot all of the other nodes.

10. Choose Start > Programs > Administrative Tools > Disk Administrator on all the nodes.

    On all nodes except the primary node, a dialog box appears, informing you the disk configuration has been detected. If you do not see this dialog box, it does not mean the disk configuration has not changed.

11. Click OK.

    The extended partition and the logical partitions are now seen by all of the nodes.

    Note: The hard disks that access the shared area may be different from node to node. The logical partitions, however, that reside on the hard disks must be identical on all nodes.

    For example, Node 1 may look like:

Figure 3-2 Node 1 Logical Partitions

Node 2 may look like:

Figure 3-3 Node 2 Logical Partitions

On Node 1, the logical partition E is defined as \Device\Harddisk1\Partition1. On Node 2, it is defined as \Device\Harddisk2\Partition1. Even though these map to different disks, they map to the same space on the shared disk.

Step 3: Unassign Drive Letters

To free up other drive letters for other purposes, such as mapping network drives, it is important to also unassign the drive letters from the logical partitions on each partition. Oracle Parallel Server does not need to access a partition through a drive letter.

Note: A two-node cluster requires 9 logical partitions, for example, with drive letters E through M. Each additional node requires two additional drives to accommodate the log files.

Note: If your disks have been previously configured, the logical partitions may already be unassigned. If this the case, you can skip to Step 6 of this procedure.

To unassign drive letters:

1. On each node, select a logical partition.

2. Choose Assign Drive Letter from the Tools menu

   The Assign Drive Letter dialog box appears:

   
   
3. Choose Do not assign a driver letter and click OK.

   A confirmation dialog box appears.

4. Click Yes to confirm change.

5. Repeat Steps 1-4 for each logical partition on each node.

6. For each node in the cluster, write down the hard disk number(s) and the number of the partition (starting at 1) for that drive.

   Note: The hard disks that access the shared area may be different from node to node. The logical partitions, however, that reside on the hard disks must be identical from node to node.

   Oracle Corporation recommends using a worksheet similar to the following.

   	Node 1	Node 2	Node 3	Node 4
   Hard Diskx	Partitions x-x	Partitions x-x	Partitions x-x	Partitions x-x
   Hard Diskx	Partitions x-x	Partitions x-x	Partitions x-x	Partitions x-x

   For example, the worksheet for the Disk Administrator windows shown in Figure 3-2, "Node 1 Logical Partitions" and Figure 3-3, "Node 2 Logical Partitions" of this chapter would look like:

   	Node 1	Node 2
   Hard Disk1	Partitions 1-6	n/a
   Hard Disk2	Partitions 1-3	Partitions 1-6
   Hard Disk3	n/a	Partitions 1-3

7. Choose Close from the Partition menu on all nodes.

   The Disk Administrator application exits.

8. Reboot each node.

9. Continue to Chapter 4, "Installing Oracle Parallel Server".