No matter what disks you have, there are always potential problems:
They can be too small.
They can be too slow.
They can be too unreliable.
Various solutions to these problems have been proposed and implemented. One way some users safeguard themselves against such issues is through the use of multiple, and sometimes redundant, disks. In addition to supporting various cards and controllers for hardware RAID systems, the base FreeBSD system includes the Vinum Volume Manager, a block device driver that implements virtual disk drives. Vinum is a so-called Volume Manager, a virtual disk driver that addresses these three problems. Vinum provides more flexibility, performance, and reliability than traditional disk storage, and implements RAID-0, RAID-1, and RAID-5 models both individually and in combination.
This chapter provides an overview of potential problems with traditional disk storage, and an introduction to the Vinum Volume Manager.
Note: Starting with FreeBSD 5, Vinum has been rewritten in order to fit into the GEOM architecture (Chapter 20), retaining the original ideas, terminology, and on-disk metadata. This rewrite is called gvinum (for GEOM vinum). The following text usually refers to Vinum as an abstract name, regardless of the implementation variant. Any command invocations should now be done using the gvinum command, and the name of the kernel module has been changed from vinum.ko to geom_vinum.ko, and all device nodes reside under /dev/gvinum instead of /dev/vinum. As of FreeBSD 6, the old Vinum implementation is no longer available in the code base.