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How Flash Pool aggregates work

In general, Flash Pool aggregates are used and managed in a similar manner as standard aggregates. However, you need to understand how both the SSD and HDD RAID groups interact and affect the rest of the system.

The SSD RAID groups, also called the SSD cache, can be composed of physical SSDs or allocation units from SSD storage pools (but not both).

The SSD cache does not contribute to the size of the aggregate as calculated against the maximum aggregate size. For example, even if an aggregate is at the maximum aggregate size, you can add an SSD RAID group to it. The SSDs do count toward the overall (node or HA pair) drive limit.

The HDD RAID groups in a Flash Pool aggregate behave the same as HDD RAID groups in a standard aggregate, following the same rules for mixing disk types, sizes, speeds, and checksums. For example, you cannot combine performance and capacity disks in the HDD RAID groups of a Flash Pool aggregate.

The checksum type, RAID type, and RAID group size values can be configured for the SSD cache RAID groups and HDD RAID groups independently. If the Flash Pool aggregate uses an SSD storage pool for its SSD cache, the cache RAID type can be changed only when the first SSD RAID groups are added, and the size of the SSD RAID groups are determined by the number of SSDs in the storage pool.

When you enable data compression manually for a volume in a Flash Pool aggregate, adaptive compression is enabled by default.

There is a platform-dependent maximum size for the SSD cache.