1. What is a naked device? Naked equipment, also called a naked partition (original partition), is a special character device that has not been formatted and not read by UNIX through the file system. It is responsible for reading and writing it by the application. No buffer of the file system. 2. How to distinguish naked equipment? In UNIX / dev directory, there are many files, including two large categories: character device files and block device files. Character equipment Special files Perform I / O operations without the buffer of the operating system, while the block device special file is used to perform a package transfer of the peripheral. Character Special Files are transmitted only one character each time when I / O operations are peripheral. For special documents for block devices, it uses a Cache mechanism to transfer a whole piece of data at a time between peripherals and memory. Naked equipment uses a character special file. In / dev directory, you can see many of this file. 3. The benefits of using naked equipment are transmitted directly from DISK to Oracle because of the use of bare devices, and the data can be transmitted directly from DISK to Oracle. performance. Of course, this is very large in the magnetic disk I / O, and the disk I / O is called the system bottleneck. If the disk read and write is indeed very frequent, so that the disk read and write becomes the system bottleneck, then the naked device can indeed greatly improve performance, up to even increase to 40%, very obvious. Moreover, since the original partition is used, there is no management method of the file system, and the overhead of the UNIX maintenance file system is not available, such as no need to maintain i-node, idle block, etc., which can also lead to improvement in performance. 4. How to decide whether naked equipment should be used? Judging whether to use bare devices to consider from the following aspects: First, the database system itself needs to be optimized. Optimization is a very technical topic, it is difficult to tell. Second, use the UNIX command to identify if there is a disk read and write bottleneck. For example, Unix's VMSTAT, SAR or other commands can be identified. If you decide to adopt a bare device, you need an idle partition on the disk. Otherwise, you should add a disk or re-plan the original system. 5. What system must use naked equipment? If you use the Oracle Parallel Server option, you must use bare devices to store all data files, control files, and redo log files. Only put these files on the bare device can ensure that all Oracle instances can read the files of this database. This is determined by the characteristics of the UNIX operating system. Another situation is that if you want to use asynchronous I / O, a naked device must also be used on some UNIX. This requires the specific UNIX related documentation. 6. Can I use a disk's first partition as a naked device? Yes, but not recommended. The old version of UNIX is a bank, and the first partition of the disk often contains some information for this disk, as well as some of the control information of the logical volume. If these parts are covered by bare devices, the disk becomes unrecognizable, causing the system to crash. New New UNIX version does not happen because they use more complex technologies to manage some information about disk, logical volumes. However, unless it is convinced that the first partition of the disk is not used as a bare device. 7. Can I use the entire bare device as an Oracle's data file? Not. The size of the data file must be slightly smaller than the actual size of the bare device. At least two Oracle blocks are available. 8. The bare equipment should belong to that user? Naked devices should be created by root and then assigned to Oracle users for use.
