Verifying the External Drive is Accessible to Each Node Oracle Database Tips by Donald Burleson

The modified kernel that allows for dual logging on the external fire-wire drive has already been installed on each node. To ensure that the drive can be accessed, run the command fdisk ‑l /dev/sda from each node as shown in Figure 5.1. The prefix sd in /dev/sda is reserved for scsi drives. The new kernel detects the external drive as the first SCSI drive.

Partitioning the External Drive

A change that is made by one node on the external drive can be read immediately by the other node. Therefore, the steps taken to partition the drive need only be done from one of the nodes.

A partition is a subdivision of the write space on a hard drive. A partition can be used to segregate different file systems. It can also be used to prevent one writing area from expanding and thus crowding out and overwriting other areas.

There are three types of partitions available: primary, extended and logical. There can be no more than four primary partitions on a single drive.

An extended partition works as a container in which to place logical partitions. Only one extended partition can be created on a drive, and an extended partition cannot be written to directly; it must be sub-divided by logical partitions.

The advantage to working with an extended partition and multiple logical partitions is that by combining the two, Linux can handle up to 15 partitions on one SCSI disk or 63 on an IDE disk.

Use the fdisk utility to partition the external drive. Call it by using the command fdisk /dev/sda as shown in Figure 5.2. There are just a few commands that need to be remembered when using fdisk.  These commands are:  help (m), print a list of partitions (p), create a new partition (n), delete a partition (d), quit without saving (q), and write a new partition table and quit (w).

To create an extended partition, type the command n for new, then respond with e for extended as shown in Figure 5.3. Type [enter] to accept the default numbers for the first and last cylinders. This will create one extended partition across the entire drive, allowing for many logical partitions to be created within that space.

Creating logical partitions within the extended partition is simple. To do this type the command n for new, then respond with l for logical as shown in Figure 5.4. This time, type [enter] to accept the default start cylinder and type +20G for the end cylinder. This action creates a new logical partition of 20 gigabytes.

A 203 gigabyte drive was used to write this book. It was divided into 11 logical partitions; the first 10 partitions were sized at 20g and the last as a smaller left-over partition.

To complete all the exercises in this book, you will need the partitions configured with the following minimum sizes in mind:

Repeat the previous command 10 times to create 11 logical partitions. View the partitions with the command p for print. A printout of your partition table should look similar to the one in Figure 5.5. You will note that the first logical partition is associated with /dev/sda5 and that its first cylinder is 1, the same as the extended partition that contains the logical partitions.

Save the configuration by typing the command w which writes the new partition table to disk and exits fdisk. At this point it is possible to quit without saving by typing the q command.

The node, which did not write the partitions, needs to update the operating system to recognize the various partitions that were just created. Switch to the alternate node, login as root and type the command partprobe and then the command fdisk ?l /dev/sda to list the partitions on the external drive. The list of partitions will match on both nodes.

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