Systems and methods for migration and recall of data from local and remote storage

In a system having access to both a local and a remote storage medium:

• wherein migration policies are used to migrate data from the local storage medium to the remote storage medium, a method of pre-migrating the data prior to fully migrating the data in a manner such that the data can be rapidly deleted from the local storage medium and migrated when migration policies associated with the data are satisfied, said method comprising the steps of:
• obtaining parameters that specify migration policies under which data is to be migrated from the local storage medium to the remote storage medium such that, when the data is migrated, the data exists at the remote storage medium and does not exist at the local storage medium, said policies comprising (1) a minimum amount of elapsed time with no access for a file to be a candidate for migration, and (2) a desired level of occupancy of the local storage medium,
• identifying at least one file stored on the local storage medium that has not yet satisfied the migration policies and is not eligible for migration from the local storage medium to the remote storage medium according to the migration policies;
• even though the migration policies have not yet been satisfied, pre-migrating data in said at least one file to the remote storage medium so that the pre-migrated data exists on the local storage medium and also exists on the remote storage medium prior to said at least one file satisfying the migration policies;
• and
• when said at least one file satisfies the migration policies, then deleting said pre-migrated data from the local storage medium so that the pre-migrated data exists only on the remote storage medium.

A method for selectively returning data of a file from a remote storage medium to a local storage medium in response to an access request for the data made after the data has been migrated from the local storage medium to the remote storage medium, the method comprising the steps of:

• storing the data of the file on the remote storage medium after the data has been migrated from the local storage medium to the remote storage medium;
• storing attributes of the file at the local storage medium;
• receiving a first access request that involves the file;
• determining that a response to the first access request can be provided using only the attributes of the file stored at the local storage medium;
• based on the determination that the response to the first access request can be provided using only the attributes of the file stored at the local storage medium, responding to the first access without recalling the data from the remote storage medium;
• then
• receiving a second access request that involves the file;
• determining that a response to the second access request can be provided only by recalling the data from the remote storage medium;
• and
• responding to the second access request by recalling the data from the remote storage medium.

A computer-readable medium having computer executable instructions for implementing a method for selectively returning data of a file from a remote storage medium to a local storage medium in response to an access request for the data made after the data has been migrated from the local storage medium to the remote storage medium, said computer readable medium comprising:

• means for storing the data of the file on the remote storage medium after the data has been migrated from the local storage medium to the remote storage medium;
• means for storing attributes of the file at the local storage medium;
• means for receiving an access request that involves the file;
• means for determining whether a response to the access request can be provided using only the attributes of the file stored at the local storage medium;
• means for responding to the access request without recalling the data from the remote storage medium if it has been determined that the response can be provided using only the attributes stored at the local storage medium;
• and
• means for responding to the access request by recalling the data from the remote storage medium if it has been determined that the response cannot be provided using only the attributes stored at the local storage medium.

A computer-readable medium having computer executable instructions for implementing, in a system having access to both a local and a remote storage medium, wherein migration policies are used to migrate data from the local storage medium to the remote storage medium, a method of pre-migrating the data prior to fully migrating the data in a manner such that the data can be rapidly deleted from the local storage medium and migrated when migration policies associated with the data are satisfied, said computer readable medium comprising:

• means for obtaining parameters that specify migration policies under which data is to be migrated from the local storage medium to the remote storage medium such that, when the data is migrated, the data exists at the remote storage medium and does not exist at the local storage medium;
• means for identifying files, including a first file, that are stored on a local storage medium and that have not yet satisfied migration policies and are not yet eligible for migration from the local storage medium to the remote storage medium;
• means for pre-migrating data stored in said first file to said remote storage medium even though the migration policies have not yet been satisfied, so that the pre-migrated data exists on said local storage medium and also exists on the remote storage medium prior to said first file satisfying the migration policies;
• means for receiving a request to write incoming data to the local storage medium prior to said first file satisfying the migration policies, the local storage medium not having sufficient free space to store the incoming data without deleting data already stored at the local storage medium;
• means for determining whether a second file that (1) contains other pre-migrated data, and (2) has satisfied the migration policies, exists on the local storage medium;
• and
• means for performing the steps of:
• if said second file exists, migrating said second file from the local storage medium to the remote storage medium so as to create said sufficient free space;
• and
• if said second file does not exist, migrating said first file from the local storage medium to said remote storage medium to create said sufficient free space notwithstanding said first file not yet satisfying the migration policies.