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server | Mail server bare devices, also called raw Partitions (original partitions), are a special character device that is not formatted and is not read by UNIX through the file system. This article collects the bare devices and Oracle Quiz 20 cases.

1. What is called a bare device?

A bare device, also called a bare partition (raw partition), is a special character device that is not formatted and is not read by UNIX through a file system. It is the responsibility of the application to read and write it. Does not pass the file system buffer.

2. How to identify the naked device?

In the Unix/dev directory, there are a number of files, including two large classes: Character device files and block device files.

Character device special files I/O operations do not go through the operating system's buffer, and the block device special files are used for fixed-length packet transmission with the peripherals. Character special files and peripherals I/O operations are transmitted only one character at a time. And for the block device special file, it uses the cache mechanism, between the peripheral and memory can transmit a whole block of data. The bare devices use character special files. You can see many of these files in the/dev directory.

3. Benefits of using bare devices

Because the use of bare devices to avoid another layer of UNIX operating system, data directly from disk to Oracle transmission, so the use of raw devices for read and write frequent database applications, can greatly improve the performance of the database system. Of course, this is only true if disk I/O is very large and disk I/O is already known as a system bottleneck. If the disk reads and writes are very frequent, so that disk reads and writes become the system bottleneck, then the use of bare devices can significantly improve performance, the maximum can be increased to 40%, very obvious.

Moreover, because the use of the original partition, no file system management, for UNIX maintenance of the file system is not the cost, such as no longer maintain i-node, free block, etc., which can also lead to improved performance.

4. How do I decide if I should use a bare device?

To determine whether to use a bare device is to consider the following: first, the database system itself needs to have been better optimized. Optimization is a very technical topic, it is difficult to simply tell. Second, use UNIX commands to identify disk read/write bottlenecks. such as Unix Vmstat, SAR and other commands can be better to identify. If you decide to adopt a bare device, you need a free partition on the disk. Otherwise, new disks will be added, or the original system should be redesigned.

5. What systems must use bare devices?

If you use the Oracle Parallel server option, you must use a bare device to store all the data files, control the files, and redo the log files. It is only possible to put these files on a bare device to ensure that all Oracle instances can read the database files. This is determined by the characteristics of the UNIX operating system.

In another case, if you want to use asynchronous I/O, you must also use a bare device on some UNIX. This requires reference to specific UNIX-related documentation.