Chapter 12 Soft Partitions (Overview)

This chapter provides information about Solaris Volume Manager soft partitions. For information about related tasks, see Chapter 13, Soft Partitions (Tasks).

This chapter contains the following information:

• Overview of Soft Partitions

• Configuration Guidelines for Soft Partitions

Overview of Soft Partitions

As the storage capacity of disks has increased, disk arrays present larger logical devices to Solaris systems. In order to create more manageable file systems or partition sizes, users might need to subdivide disks or logical volumes into more than eight partitions. Solaris Volume Manager's soft partition feature addresses this need.

Solaris Volume Manager can support up to 8192 logical volumes per disk set. This number includes the local, or unspecified, disk set. Solaris Volume Manager configures volumes dynamically as they are needed.

You can use soft partitions to divide a disk slice or logical volume into as many partitions as needed. You must provide a name for each division, or soft partition, just like you do for other storage volumes, such as stripes or mirrors. A soft partition, once named, can be accessed by applications, including file systems, as long as the soft partition is not included in another volume. Once included in a volume, the soft partition should no longer be directly accessed.

Soft partitions can be placed directly above a disk slice, or on top of a mirror, stripe, or RAID-5 volume. A soft partition may not be both above and below other volumes. For example, a soft partition built on a stripe with a mirror built on the soft partition is not allowed.

A soft partition appears to file systems and other applications as a single contiguous logical volume. However, the soft partition actually comprises a series of extents that could be located at arbitrary locations on the underlying media. In addition to the soft partitions, extent headers (also called system recovery data areas) on disk record information about the soft partitions to facilitate recovery in the event of a catastrophic system failure.

Configuration Guidelines for Soft Partitions

• Slices that are used for soft partitions cannot be used for other purposes.

• When you partition a disk and build file systems on the resulting slices, you cannot later extend a slice without modifying or destroying the disk format. Soft partitions behave differently. You can extend a soft partition up to the amount of space on the underlying device without moving or destroying data on other soft partitions.

• While it is technically possible to manually place extents of soft partitions at arbitrary locations on disk, you should allow the system to place them automatically. For an example of an extent that has been manually placed, see the output of the metastat command in Viewing the Solaris Volume Manager Configuration.

• You can build soft partitions on any slice. However, creating a single slice that occupies the entire disk and then creating soft partitions on that slice is the most efficient way to use soft partitions at the disk level.

• The maximum size of a soft partition is limited to the size of the slice or logical volume on which it is built. Because of this limitation, you should build a volume on top of your disk slices, then build soft partitions on top of the volume. This strategy allows you to add components to the volume later, and then expand the soft partitions as needed.

• For maximum flexibility and high availability, build RAID-1 (mirror) or RAID-5 volumes on disk slices, then create soft partitions on the mirror or RAID-5 volume.

Scenario—Soft Partitions

Soft partitions provide tools with which to subdivide larger storage spaces into more manageable spaces. For example, in other scenarios (Scenario—RAID-1 Volumes (Mirrors) or Scenario—RAID-5 Volumes), large storage aggregations provided redundant storage of many gigabytes. However, many possible scenarios would not initially, require so much space. Soft partitions allow you to subdivide that storage space into more manageable partitions. Each of those partitions can have a complete file system. For example, you could create 1000 soft partitions on top of a RAID-1 or RAID-5 volume so that each of your users can have a home directory on a separate file system. If a user needs more space, you could simply expand the soft partition.