TAILIEUCHUNG - Chapter-12-The Vinum Volume Manager

The way the data is shared across the drives has a strong influence on performance. It’s convenient to think of the disk storage as a large number of data sectors that are addressable by number, rather like the pages in a book. The most obvious method is to divide the virtual disk into groups of consecutive sectors the size of the individual physical disks and store them in this manner, rather like the way a large encyclopaedia is divided into a number of volumes. This method is called concatenation, and sometimes JBOD (Just a Bunch Of Disks). It works well when the access to the virtual. | 10 April 2003 06 13 07 The Complete FreeBSD page 221 In this chapter Vinum objects Creating Vinum drives Starting Vinum Configuring Vinum Vinum configuration database Installing FreeBSD on Vinum Recovering from drive failures Migrating Vinum to a new machine Things you shouldn t do with Vinum 12 The Vinum Volume Manager Vinum is a Volume Manager a virtual disk driver that addresses these three issues Disks can be too small. Disks can be too slow. Disks can be too unreliable. From a user viewpoint Vinum looks almost exactly the same as a disk but in addition to the disks there is a maintenance program. Vinum objects Vinum implements a four-level hierarchy of objects The most visible object is the virtual disk called a volume. Volumes have essentially the same properties as a UNIX disk drive though there are some minor differences. They have no size limitations. Volumes are composed of plexes each of which represents the total address space of a volume. This level in the hierarchy thus provides redundancy. Think of plexes as individual disks in a mirrored array each containing the same data. Vinum exists within the UNIX disk storage framework so it would be possible to use UNIX partitions as the building block for multi-disk plexes but in fact this turns out v 2003 04 09 19 56 42 221 10 April 2003 06 13 07 The Complete FreeBSD . tools page 222 222 Chapter 12 The Vinum Volume Manager to be too inflexible UNIX disks can have only a limited number of partitions. Instead Vinum subdivides a single UNIX partition the drive into contiguous areas called subdisks which it uses as building blocks for plexes. Subdisks reside on Vinum drives currently UNIX partitions. Vinum drives can contain any number of subdisks. With the exception of a small area at the beginning of the drive which is used for storing configuration and state information the entire drive is available for data storage. Plexes can include multiple subdisks spread over all drives

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