General ZFS Storage Pool Requirements

The following sections describe ZFS root pool space and configuration requirements.

Disk Space Requirements for ZFS Storage Pools

The required minimum amount of available pool space for a ZFS root file system is larger than for a UFS root file system because swap and dump devices must be separate devices in a ZFS root environment. By default, swap and dump devices are the same device in a UFS root file system.

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 upon the amount of physical memory. The minimum amount of available pool space for a bootable ZFS root file system depends upon the amount of physical memory, the disk space available, and the number of boot environments (BEs) to be created.

Review the following disk space requirements for ZFS storage pools:

• 768 MB is the minimum amount of memory required to install a ZFS root file system.

• 1 GB of memory is recommended for better overall ZFS performance.

• At least 16 GB of disk space is recommended. The disk space is consumed as follows:

  • Swap area and dump device – The default sizes of the swap and dump volumes that are created by the Solaris installation programs are as follows:

    • Solaris initial installation – In the new ZFS boot environment, the default swap volume size is calculated as half the size of physical memory, generally in the 512 MB to 2 GB range. You can adjust the swap size during an initial installation.

    • The default dump volume size is calculated by the kernel based on dumpadm information and the size of physical memory. You can adjust the dump size during an initial installation.

    • Oracle Solaris Live Upgrade – When a UFS root file system is migrated to a ZFS root file system, the default swap volume size for the ZFS BE is calculated as the size of the swap device of the UFS BE. The default swap volume size calculation adds the sizes of all the swap devices in the UFS BE, and creates a ZFS volume of that size in the ZFS BE. If no swap devices are defined in the UFS BE, then the default swap volume size is set to 512 MB.

    • In the ZFS BE, the default dump volume size is set to half the size of physical memory, between 512 MB and 2 GB.

    You can adjust the sizes of your swap and dump volumes to sizes of your choosing as long as the new sizes support system operations. For more information, see Adjusting the Sizes of Your ZFS Swap Device and Dump Device.

  • Boot environment (BE) – In addition to either new swap and dump space requirements or adjusted swap and dump device sizes, a ZFS BE that is migrated from a UFS BE requires approximately 6 GB. Each ZFS BE that is cloned from another ZFS BE doesn't require additional disk space, but consider that the BE size will increase when patches are applied. All ZFS BEs in the same root pool use the same swap and dump devices.

  • Solaris OS Components – All subdirectories of the root file system that are part of the OS image, with the exception of /var, must be in the same dataset as the root file system. In addition, all Solaris OS components must reside in the root pool, with the exception of the swap and dump devices.

    Another restriction is that the /var directory or dataset must be a single dataset. For example, you cannot create a descendent /var dataset, such as /var/tmp, if you want to also use Oracle Solaris Live Upgrade to migrate or patch a ZFS BE or create a ZFS flash archive of this pool.

  For example, a system with 12 GB of disk space might be too small for a bootable ZFS environment because 2 GB of disk space is required for each swap and dump device and approximately 6 GB of disk space is required for the ZFS BE that is migrated from the UFS BE.

ZFS Storage Pool Configuration Requirements

Review the following ZFS storage pool configuration requirements:

• The pool that is intended to be the root pool must have an SMI label. This requirement is met if the pool is created with disk slices.

• The pool must exist either on a disk slice or on disk slices that are mirrored. If you attempt to use an unsupported pool configuration during an Oracle Solaris Live Upgrade migration, you see a message similar to the following:

  ERROR: ZFS pool name does not support boot environments

  For a detailed description of supported ZFS root pool configurations, see Creating a ZFS Root Pool.

• x86: The disk must contain a Solaris fdisk partition. A Solaris fdisk partition is created automatically when the x86 based system is installed. For more information about Solaris fdisk partitions, see Guidelines for Creating an fdisk Partition in System Administration Guide: Devices and File Systems.

• Disks that are designated for booting in a ZFS root pool must be limited to 1 TB in size on both SPARC based and x86 based systems.

• Compression can be enabled on the root pool but only after the root pool is installed. No way exists to enable compression on a root pool during installation. The gzip compression algorithm is not supported on root pools.

• Do not rename the root pool after it is created by an initial installation or after Solaris Live Upgrade migration to a ZFS root file system. Renaming the root pool might cause an unbootable system.