netapp storage tiering

see http://media.netapp.com/documents/tr-4070.pdf
and http://media.netapp.com/documents/wp-7127.pdf


A Flash Pool is the newest addition to the NetApp® Virtual Storage Tier. It is a technology that allows Flash technology in the form of solid-state disks (SSDs) and traditional hard disk drives (HDDs) to be combined to form a single Data ONTAP® aggregate.

Essentially it is the addition of SSDs into an aggregate to provide a high-bandwidth, lowlatency location that is capable of caching random reads and random overwrites. The feature does not require a license and works with any NetApp SSDs and one type of HDD per Flash Pool. That is, SSD and SAS performance drives can be combined to make a Flash Pool, or  SSD and SATA capacity drives can be combined to make a Flash Pool. You cannot combine SSD, SAS, and SATA into a single Flash Pool.

Only one type of spinning drive can be combined with SSDs to create a Flash Pool. For example, it’s acceptable to have SATA and SSD, or you can have SAS (or FC) and SSD. The combination of SATA and SAS and SSD is not allowed in the same aggregate.

A Flash Pool can only be created from 64-bit aggregates. You cannot create a 32-bit Flash Pool or convert an existing 32-bit aggregate into a Flash Pool.
Once the SSDs are placed in a Flash Pool they are required in that aggregate as long as it exists.
Flash Pool is available starting in Data ONTAP 8.1.1 operating in both 7-Mode and ClusterMode.

The SSDs do not increase the storage capacity of the aggregate. The SSD space is used to cache the most frequently accessed data. It does not add any user-visible space to the aggregate.
You can mix SATA and SSD in the same DS4243 shelf. You cannot mix SSD and SAS drives in the same shelf.

A Flash Pool cannot be reversed to a normal aggregate. The data must be copied to another location and the Flash Pool aggregate destroyed and rebuilt. The data can then be copied back..

For FAS3100 and FAS3200 series that support Flash Pool, the recommended minimum number of SSDs is a 3+2 (3 data + 2 parity) RAID group. (This assumes NetApp RAID-DP ® protection.)