Stand-in Computer file server providing fast recovery from computer file server failures

Claim 1

A hierarchical storage system for protecting a protected set of files stored on a plurality of file servers of a computer network of computer nodes, each file server having a direct-access mass storage device (DASD) storing the files, the contents of the files read and altered by an external process running on computers of the network, the system comprising: a storage manager configured to snapshot recently-altered files (a) from the file servers' DASD's to a DASD of an integrity server, (b) and then from the integrity server's DASD to removable mass storage media, the integrity server's DASD being of a size much less than a sum of the sizes of the file servers' DASD's, wherein a retention time of a file version in the integrity server's DASD depends on characteristics of the external process' access to the corresponding file, and wherein each file is copied to said removable media within a short time after being altered on a file server's DASD to produce a new current version; and a retrieval manager providing to the external process access to the file copies as a stand-in for the files of an unavailable file server, said retrieval manager configured to be activated when unavailability of one of the file servers is detected, and to copy current versions of files not then resident on the integrity server's DASD from said removable media to the integrity server's DASD.

Claim 6

A method for use in servicing file demands to a hierarchical file system on a direct access storage device (DASD), comprising the computer-implemented steps of: providing on non-direct access storage media a copy of the files of the file system; for each directory traversed in response to a file demand on a demanded file access path, automatically and without human intervention: if a directory corresponding to the traversed directory does not already exist on the DASD, creating a directory corresponding to the traversed directory on the DASD, and servicing the file demand using the created directory; and if a directory corresponding to the traversed directory does already exist on the DASD, servicing the file demand using the existing corresponding directory.

Claim 7

A method for use in servicing file demands to a hierarchical file system on a direct access storage device (DASD), comprising the computer-implemented steps of: providing on non-direct access storage media a copy of the files of the file system; for each directory traversed in response to a file demand on a demanded file access path, automatically and without human intervention: if a directory corresponding to the traversed directory does not already exist on the DASD, creating a directory corresponding to the traversed directory on the DASD, and servicing the file demand using the created directory; and if a directory corresponding to the traversed directory does already exist on the DASD, servicing the file demand using the existing corresponding directory.