RAID 5 volumes allow you to have redundant storage without the overhead of RAID 1 volumes, which require two times the total storage space to provide data redundancy. By setting up a RAID 5 volume, you can provide redundant storage of greater capacity than you could achieve with RAID 1 on the same set of disk components, and, with the help of hot spares (see Chapter 16, Hot Spare Pools (Overview) and specifically How Hot Spares Work), nearly the same level of safety. The drawbacks are increased write time and markedly impaired performance in the event of a component failure, but those trade-offs might be insignificant for many situations. The following example, drawing on the sample system explained in Chapter 5, Configuring and Using Solaris Volume Manager (Scenario), describes how RAID 5 volumes can provide extra storage capacity.
Other scenarios for RAID 0 and RAID 1 volumes used 6 slices (c1t1d0, c1t2d0, c1t3d0, c2t1d0, c2t2d0, c2t3d0) on six disks, spread over two controllers, to provide 27 Gbytes of redundant storage. By using the same slices in a RAID 5 configuration, 45 Gbytes of storage is available, and the configuration can withstand a single component failure without data loss or access interruption. By adding hot spares to the configuration, the RAID 5 volume can withstand additional component failures. The most significant drawback to this approach is that a controller failure would result in data loss to this RAID 5 volume, while it would not with the RAID 1 volume described in Scenario—RAID 1 Volumes (Mirrors).