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System Administration Guide Supplement for SunOS Release 4.x (BSD)

Chapter 3: Choosing Database Devices

Chapter 3

Choosing Database Devices

Database devices are files or portions of a disk that are used to store databases and database objects. You can initialize devices using regular operating system files or raw partitions.

The sybinit utility initializes the master and auditing devices for a SQL Server during the installation session. See the SQL Server Installation Guide for instructions on using sybinit to initialize the master device, named sybsystemprocs , and the auditing devices.

You can use the disk init command to initialize additional devices after your SQL Server installation is complete. See the System Administration Guide for detailed information on disk init . This chapter focuses on choosing database devices to initialize with disk init and discusses:

• Using raw partitions for database devices

• Selecting raw partitions

• Preparing raw partitions to be database devices

• Preparing operating system files to be database devices

• Using network-mounted files for database devices

Raw Partition or Operating System File?

Raw partition installations are recommended for production databases because of their recovery capabilities and increased processing performance.

Regular operating system file devices are recommended only for testing and fine-tuning databases, as these devices pose a risk of database corruption in the event of a media failure, power failure, or system panic. Under these circumstances, SQL Server cannot guarantee recovery, since information in the I/O buffer is frequently lost.

If you install your master database device on an operating system file, you can still initialize raw partitions to be used as additional database devices. If you install your master device on a raw partition, you can initialize operating system files to be used as additional database devices.

Using Raw Partitions for Database Devices

Warning! When you initialize a raw partition for use as a SQL Server database or log device, you destroy any existing files on that partition. Do not initialize a database device on the partition that contains your SYBASE software.

Once sybinit or disk init has initialized a portion of a partition as a database device, that partition cannot be used for any other purpose, including other SYBASE uses. Any space left on the partition beyond the size of the device you specified during disk init becomes inaccessible. For example, if you initialize a 10MB database device on a 50MB partition, you cannot use the remaining 40MB, unless you drop and recreate the device.

Guidelines for Choosing a Raw Partition

When you choose a raw partition, consider the following guidelines:

• Do not choose a partition containing the partition map, which is usually in the first sector of the first cylinder. To avoid the possibility of using a partition that contains the partition map, do not use cylinder "0".

• A raw partition specified for SQL Server should not be mounted for use by the operating system, as it cannot be used for any other purpose, such as for file systems or swap space.

• A user with the System Administrator role should own the disk partition, and should have read and write permissions on it, because a System Administrator must issue the disk init command to initialize a database device. See your operating system documentation for information on changing ownership and permissions.

  Note: The user who boots SQL Server before the disk init command is issued must have read and write permissions on the partition.

Character and Block Devices

A partition can be accessed through two different types of devices, a character device or a block device. All I/O to the partition is done through one of these devices.

SQL Server uses the character device (sometimes called the "raw" device) because the SQL Server recovery system needs unbuffered system I/O. Use the character device name for any raw partition that you use for a database device.

Preparing Raw Partition Devices

Log in as a System Administrator user to select and prepare a partition to be a database device:

Using Operating System Files for Database Devices

If you want to use an operating system file for a database device to be initialized by disk init , consider the following:

• The directory for the file must exist before you initialize the device. If the directory is not created before initialization, the root directory will fill up. disk init does not create the directory for you: it creates the file.

• You must specify the absolute path name of the file for disk init . If a file with the same name as the device already exists in the directory, SQL Server prints an error message and does not initialize the device.

• A user with the System Administrator role should have read, write, and execute permissions on the directory, because the System Administrator issues the disk init command.

  Note: The user who boots the SQL Server before the disk init command is issued must also have read, write, and execute permissions on the directory.

Preparing Operating System File Devices

1. Use the df command to ensure there is enough space available on the file system for the device.

2. Create the device directory if it does not exist.

3. Make sure that a user with the System Administrator role owns the directory and has read, write, and execute permissions on it. Consult your operating system documentation for information on commands you can use to change ownership and permissions.

Using Network-Mounted Files As Database Devices

• Network problems can cause serious data integrity problems, because the network lies between SQL Server and the devices on which it writes.

• To run SQL Server using network-mounted files as database devices, you must use operating system files. Devices installed on files cannot guarantee recovery in the event of a media failure, power failure, or system panic. Raw partition installations have better recovery capabilities and increased processing performance.

• If the remote machine is down when you reboot SQL Server, and the database devices cannot be activated, automatic recovery will fail.

• SQL Server is suspended when the remote machine or network is down.

What's Next?

Chapter 4 describes operating system issues that you must consider in order to run SQL Server.