Patent ID: 8055724

Claim:
A method of operating a file server in a data network for access to file data that is migrated between primary storage and secondary storage, the file server responding to a client request for read access to a specified file by checking whether file data of the specified file has been migrated from the primary storage to the secondary storage, and upon finding that file data of the specified file has been migrated from the primary storage to the secondary storage, selecting a particular one of a number of offline file read access methods that are selectable by the file server under various conditions, the offline file read access methods including a partial read migration method for migrating only a portion of the data of an offline file from the secondary storage to the primary storage for retention in the primary storage after client read access, and a pass-through method in which the file server obtains file data from the secondary storage and passes on to a client the file data obtained from the secondary storage without retention in the primary storage of the file data obtained from the secondary storage; which further includes the file server responding to a request to truncate a partially migrated offline file to a new offset that is less than an extent of the partially migrated offline file, the file server responding to the request to truncate the partially migrated offline file by checking whether data of the partially migrated offline file up to the new offset is presently resident in the primary storage of the file server, and upon finding that data of the partially migrated offline file up to the new offset is presently resident in the primary storage of the file server, truncating the partially migrated offline file to the new offset by setting the extent of the partially migrated offline file to the new offset, and setting the partially migrated offline file to online status.