When you have the storage array assembled, use the storage management software to group a collection of drives into one or more disk pools, volume groups, or a mix of disk pools and volume groups. Disk pools and volume groups can coexist on the same storage array, but cannot share the same set of drives.
Each disk pool and volume group consist of a unique set of drives. You use the storage management software to logically group the drives together to provide one or more volumes to an application host. All of the drives in a disk pool or volume group must be of the same media type: either solid state disks (SSDs) or hard disk drives (HDDs).
In general, disk pools are easier to configure and maintain. Most of the configuration settings for a disk pool are set automatically, such as the RAID level, and you do not have to configure a hot spare drive. Adding drives to a disk pool is a simpler and faster process than adding drives to a volume group. You can add up to 12 drives to a disk pool at one time as compared to adding one drive to a volume group at one time. The exception to this rule is when using RAID 10, where two drives are added to a volume group at one time.
Disk pools and volume groups have these differences:
A disk pool is a collection of 11 or more drives in a storage array that have the same spindle speed, the same security level, and preferably the same capacity to make the most efficient use of the drives. A storage array can contain one or more disk pools, although the benefits of using a disk pool increase as the number of drives in a disk pool increase.
Creating a disk pool with the largest number of similar drives is the preferred approach. However, if not all drives in the storage array have the same characteristics or if you want certain drives to support different applications, you can create more than one disk pool on your storage array. In most cases, there is no practical limit on the number of drives that can comprise a disk pool, although a disk pool cannot contain more drives than the maximum limit for each storage array.
If a drive fails in a disk pool, all of the other operational drives in the disk pool participate in the reconstruction process. The reconstruction data space is used to reconstruct the data from the failed drive.
A volume group is a collection of drives in a storage array that have the same spindle speed, the same security level, the same type of drive media (HDD or SSD), and preferably the same capacity to make the most efficient use of the drives. The minimum and maximum number of drives that can comprise a volume group depends on the RAID level you plan to assign to the volume group.
A storage array can contain one or more volume groups. You can create several volume groups if the drives in your storage array have different characteristics (Data Assurance or Full Disk Encryption), if you want to use different RAID levels, or if you want certain drives to support different applications. When you create a volume group, you assign a RAID level. This RAID level determines how redundancy or parity data is stored on the drives that comprise the volumes within the volume group.
When you create a volume group, you can create a hot spare drive to support a volume group. A hot spare is a drive, containing no data, that acts as a standby in case a drive fails. Hot spares are assigned globally, not to a specific volume group. The hot spare drive will not be part of the volume group but must be available for the volume group to use in the event of a disk failure. The hot spare drive should match the characteristics of the drives in the volume group; otherwise, some of the capacity of the hot spare is not used.
When a host operating system writes data to the volumes within a volume group, the user data and redundancy or parity data are distributed across the drives in a volume group. Information about data locations is maintained by the controller. If a drive fails within a volume group, a hot spare drive takes over for the failed drive and is used in the data recovery process. To recover the data from the failed drive, the controller uses redundancy or parity data, which is stored based on the RAID level assigned to a volume group.