Patent ID: 8271733

Claim:
A storage apparatus for storing data, said storage apparatus comprising: a plurality of stores having storage locations for storing data items, said stores including at least one level one store and a level two store, said storage apparatus having a hierarchy such that, in response to an access request for accessing a data item, at least one of said at least one level one store is accessed and, in response to detecting that said item is not stored in said one of said at least one level one store, said level two store is accessed; said storage apparatus is configured to store a copy of at least one data item in both of said at least one level one store and said level two store, said storage apparatus comprising a plurality of indicator storage elements associated with a corresponding plurality of storage locations of said level two store, a set value of an indicator stored in one of said indicator storage elements indicating that said at least one data item is also stored in said at least one level one store, wherein said storage apparatus is configured such that, in response to request to allocate a storage location in said level two store, storage locations having a said set value of said indicator are not selected for eviction.