Normally, on a system with a UFS root file system, swap and dump are on the same slice. Therefore, UFS shares the swap space with the dump device. In a ZFS root pool, swap and dump are separate zvols, so they do not share the same physical space. When a system is installed or upgraded with a ZFS root file system, the size of the swap area and the dump device are dependent on the amount of physical memory. The minimum amount of available pool space for a bootable ZFS root file system depends on the amount of physical memory, the disk space available, and the number of boot environments to be created. Approximately 1 Gbyte of memory and at least 2 Gbytes of disk space are recommended. The space is consumed as follows:
Swap area and dump device - The default size of swap is 1/2 the size of physical memory, but no less than 512 Mbytes and no greater than 2 Gbytes. The dump device is calculated based on the size of the memory and the contents of the dumpadm.conf file. This file defines what goes into a crash dump. You can adjust the sizes of your swap and device volumes before or after installation. For more information, see Introducing ZFS Properties in Solaris ZFS Administration Guide.
Boot environments - In addition to either new swap and dump space requirements or adjusted swap and dump device sizes, a ZFS boot environment that is migrated from a UFS boot environment needs approximately 6 Gbytes. Each ZFS boot environment that is cloned from another ZFS boot environment does not need additional disk space. However, the boot environment size might increase when patches are applied. All ZFS boot environments in the same root pool use the same swap and dump devices.