With standard disk devices, each disk slice has its own physical and logical device. In addition, with standard Solaris file systems, a file system cannot span more than one disk slice. In other words, the maximum size of a file system is limited to the size of a single disk. On a large server with many disk drives, standard methods of disk slicing are inadequate and inefficient. This was a limitation in all Unix systems until the introduction of virtual disks, also called virtual volumes. To eliminate the limitation of one slice per file system, there are virtual volume management packages that are able to create virtual volume structures in which a single file system can consist of nearly an unlimited number of disks or partitions. The key feature of these virtual volume management packages is that they transparently provide a virtual volume that can consist of many physical disk partitions. In other words, disk partitions are grouped across several disks to appear as one single volume to the operating system.
Each flavor of Unix has its own method of creating virtual volumes, and Sun has addressed virtual volume management with their Solaris Volume Manager product called SVM, which is included as part of the standard Solaris 10 release.
The objectives in the Part II exam have changed so that you are now required to be able to set up virtual disk volumes. This chapter introduces you to SVM and describes SVM in enough depth to meet the objectives of the certification exam. It is by no means a complete reference for SVM.
Also in this chapter, we have included a brief introduction of Veritas Volume Manager, an unbundled product that is purchased separately. Even though this product is not specifically included in the objectives for the exam, it provides some useful background information.