A system comprising: a host adapted to run a higher layer application; a storage array controller apparatus comprising: a host interface to the host; a storage array interface to a physical array; and a thin-provisioning module adapted to receive a command over the host interface, the command specifying an extent to be thinly provisioned in the physical array, and characterized in that the thin-provisioning module is adapted to set thin-provisioning mode information for the extent indicating that the extent is to be filled with a specific data type, wherein the specific data type specifies random numbers or zero fill; wherein the thin-provisioning mode information further comprises, for each extent, one or more LBAs, whether or not a corresponding LUN is thinly provisioned, whether the specific data type is zero or random, whether or not the extent is materialized, and/or a random number seed; upon a request from the host, causes the storage array to materialize the extent as specified by the corresponding thin-provisioning information; and wherein, upon a request is being made by the higher layer application to write random data in a LUN extent prior to writing encrypted data to the LUN extent, the storage array controller is adapted to reply with thin-provisioning mode information of said extent, and wherein, if the LUN's extent is already materialized and pre-filled with random data, the thin-provisioning mode information is usable by the application to determine to refrain from generating and filling the LUN's extent with random data. a host adapted to run a higher layer application; a storage array controller apparatus comprising: a host interface to the host; a storage array interface to a physical array; and a thin-provisioning module adapted to receive a command over the host interface, the command specifying an extent to be thinly provisioned in the physical array, and characterized in that the thin-provisioning module is adapted to set thin-provisioning mode information for the extent indicating that the extent is to be filled with a specific data type, wherein the specific data type specifies random numbers or zero fill; wherein the thin-provisioning mode information further comprises, for each extent, one or more LBAs, whether or not a corresponding LUN is thinly provisioned, whether the specific data type is zero or random, whether or not the extent is materialized, and/or a random number seed; upon a request from the host, causes the storage array to materialize the extent as specified by the corresponding thin-provisioning information; and wherein, upon a request is being made by the higher layer application to write random data in a LUN extent prior to writing encrypted data to the LUN extent, the storage array controller is adapted to reply with thin-provisioning mode information of said extent, and wherein, if the LUN's extent is already materialized and pre-filled with random data, the thin-provisioning mode information is usable by the application to determine to refrain from generating and filling the LUN's extent with random data. a host interface to the host; a storage array interface to a physical array; and a thin-provisioning module adapted to receive a command over the host interface, the command specifying an extent to be thinly provisioned in the physical array, and characterized in that the thin-provisioning module is adapted to set thin-provisioning mode information for the extent indicating that the extent is to be filled with a specific data type, wherein the specific data type specifies random numbers or zero fill; wherein the thin-provisioning mode information further comprises, for each extent, one or more LBAs, whether or not a corresponding LUN is thinly provisioned, whether the specific data type is zero or random, whether or not the extent is materialized, and/or a random number seed; upon a request from the host, causes the storage array to materialize the extent as specified by the corresponding thin-provisioning information; and wherein, upon a request is being made by the higher layer application to write random data in a LUN extent prior to writing encrypted data to the LUN extent, the storage array controller is adapted to reply with thin-provisioning mode information of said extent, and wherein, if the LUN's extent is already materialized and pre-filled with random data, the thin-provisioning mode information is usable by the application to determine to refrain from generating and filling the LUN's extent with random data.