1.2.4 Storage Pools

Exascale uses pool disks and storage pools to organize the physical storage provided by Exadata storage servers.

An Exascale storage pool is a collection of pool disks that provides persistent physical storage for Exascale vaults and files. Each storage pool is a collection of pool disks using only one type of storage media (for example, HC). You cannot define a storage pool with pool disks having a mixture of media types (for example, HC and EF).

A working Exascale system requires at least one storage pool and can accommodate many storage pools. However, there is no need to define multiple storage pools for data separation because Exascale vaults provide strong data isolation.

A storage pool can contain pool disks that reside on different generations of Exadata storage server hardware, which allows for easy migration to new generations of Exadata hardware.

You can dynamically reconfigure a storage pool by changing the size of the pool disks or by adding or removing pool disks (or Exadata storage servers). However, you should pay attention to these recommendations:

• For each storage pool, use pool disks that are spread across all of the available storage devices in each storage server.

• On each storage server, maintain consistent sizing for all of the pool disks belonging to a storage pool. However, within a storage pool, pool disks on different storage servers can have different sizes.

Internally, a storage pool contains separate areas known as storage pool rings. Furthermore, the physical storage is arranged into smaller groups of pool disks and their associated storage servers, known as disk partner groups and cell partner groups.

The disk and cell partner groups maximize availability by limiting the potential effects of multiple simultaneous failures. This is because the probability of multiple simultaneous failures within a small group is much lower than the probability of multiple simultaneous failures anywhere across a large system. Also, simultaneous failures affecting different groups can be handled independently within each group.

Furthermore, Exascale uses separate storage pool rings for data and recovery files. The organization of the storage pool rings guarantees that data file extents and related recovery files automatically use different disk partner groups. So, in the unlikely event that multiple failures affect a data file, its corresponding recovery files remain available.

You cannot specify or change the internal organization of the storage pool rings or the cell and disk partner groups. However, Exascale provides information about these constructs, which is helpful for monitoring the system and understanding the impact of any storage failure scenario.