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Part III. System Administration
Chapter 19. GEOM: Modular Disk Transformation Framework
GEOM: Modular Disk Transformation Framework GEOM: 模組化磁碟轉換框架
Synopsis 概述
In FreeBSD, the GEOM framework permits access and control to classes, such as Master Boot Records and BSD labels, through the use of providers, or the disk devices in [.filename]#/dev#. By supporting various software RAID configurations, GEOM transparently provides access to the operating system and operating system utilities.
This chapter covers the use of disks under the GEOM framework in FreeBSD. This includes the major RAID control utilities which use the framework for configuration. This chapter is not a definitive guide to RAID configurations and only GEOM-supported RAID classifications are discussed.
After reading this chapter, you will know: 讀完這章,您將了解:
What type of RAID support is available through GEOM.
How to use the base utilities to configure, maintain, and manipulate the various RAID levels.
How to mirror, stripe, encrypt, and remotely connect disk devices through GEOM.
How to troubleshoot disks attached to the GEOM framework.
Before reading this chapter, you should: 在開始閱讀這章之前,您需要:
Understand how FreeBSD treats disk devices (crossref:disks[disks,Storage]).
Know how to configure and install a new kernel (crossref:kernelconfig[kernelconfig,Configuring the FreeBSD Kernel]).
RAID0 - Striping RAID0 - 串連 (Striping)
Striping combines several disk drives into a single volume. Striping can be performed through the use of hardware RAID controllers. The GEOM disk subsystem provides software support for disk striping, also known as RAID0, without the need for a RAID disk controller.
In RAID0, data is split into blocks that are written across all the drives in the array. As seen in the following illustration, instead of having to wait on the system to write 256k to one disk, RAID0 can simultaneously write 64k to each of the four disks in the array, offering superior I/O performance. This performance can be enhanced further by using multiple disk controllers. 在 <acronym>RAID0</acronym> 中,資料會被切割成數個資料區塊 (Block) 寫入到磁碟陣列中的每一個磁碟機。如下圖所示,取代以往等候系統寫入 256k 到一個磁碟的時間, <acronym>RAID0</acronym> 可以同時寫入 64k 到磁碟陣列中四個磁碟的每個磁碟,這可提供優異的 <acronym>I/O</acronym> 效能,若使用多個磁碟控制器可增加更多的效能。
Disk Striping Illustration
striping.png
Each disk in a RAID0 stripe must be of the same size, since I/O requests are interleaved to read or write to multiple disks in parallel.