Abstract: A method and apparatus for recovery from faults in a loop network (500) is provided. The loop network (500) has a plurality of ports (520, 530, 532, 534) serially connected with means for bypassing the ports (520, 530, 532, 534) from the loop network (500). A control device (522, 524) is provided with bypass control over at least one of the ports (530, 532, 534). A host means (502) sends a command to the control device (522, 524) at regular intervals and the control device (522, 524) has a counter which restarts a time period at the receipt of each command. If the time period expires, the control device (522, 524) activates the means for bypassing all the ports (530, 532, 534) under its control. The loop network (500) may have two loops (516, 518) with at least some of the ports (520, 530, 532, 534) common to both loops (516, 518).

Abstract: A method and apparatus for recovery from faults in a loop network (400) is provided. The loop network (400) has a host means (402), a first loop and a second loop (406, 408), a plurality of ports (410) connected to each of the loops (406, 408) and a control device (414, 440) on or connected to each loop (406, 408) with bypass control over at least one of the ports (410) connected to the loop (406, 408). In the event of a failure on the first loop (406), the host means (402) instructs the bypassing of at least one port (410) on the first loop (406), the host means (402) sending the instructions via the control device (414, 440) on or connected to the second loop (408).

Abstract: A log structured array (LSA) controller apparatus controls the transfer of information between a processor and a plurality of information storage devices configured as an N+1 array in which the information is stored as stripes extending across the devices of the array, each stripe comprising N information strips and one parity strip, each information strip storing an integer number of logical tracks. The controller defines an LSA directory that specifies the location of each logical track in terms of the ID of the stripe to which the track belongs and the offset of the track within the stripe; wherein on the addition of an information storage device to the array, the additional strip provided for each stripe by the storage device is logically appended to the end of each stripe in the LSA directory.

Abstract: A data storage system (100) and a method of storing data are described including a cache (118) with a variable number of levels (210, 220, 230, 240). Each level in the cache (118) has a cache controller (212, 222, 232, 242) and a cache memory (214, 224, 234, 244) for storing data. An address mapping is recorded and applied between each of the levels of the cache (118). The address mapping corresponds to a point in time virtual copy operation such as a snapshot copy operation applied to the cache (118) and enables point in time virtual copy operations to be carried out in electronic time. A new level is created in the cache (118) when a point in time virtual copy operation is received by the cache and a corresponding address mapping is applied to the previous level in the cache (118).

Abstract: A method for rebuilding meta-data stored in a data storage system (104) having storage devices (106) in which segments of data are located; for example, a storage system in the form of a log structured array. Data is written in segments to the storage devices (106) from a plurality of flows (122) of data and each segment of data contains meta-data relating to that segment. The meta-data stored in the storage system (104) can be rebuilt in the event of a failure by scanning the meta-data in each segment. A first scan of the meta-data in each segment in the storage devices (106) identifies the last segment written from each flow (122) and these segments are excluded from the rebuilding process as they may contain incomplete or inconsistent information. A second scan of the meta-data in each segment in the storage devices (106) identifies any segments which do not contain any live data tracks and these segments are also excluded from the, rebuilding process.

Abstract: A data storage system and method of storing data with at least two controllers (200, 300) which share a storage space (244, 344) on an array of storage devices and which support the same set of logical upstream devices. The controllers (200, 300) share the workload by dividing the shared storage space (244, 344) into stripes where the stripes are sufficiently small to divide the workload uniformly across the storage device. This is achieved in the case of two controllers (200, 300) of a log structured array by dividing the storage space into odd and even tracks, all odd tracks being designated to one controller (300) and all even tracks to the other controller (200).

Abstract: An analyzer for a storage network attached to a host computer system through multiple controllers receives information from each controller concerning a shared storage network bus, and resolves incomplete information received from one controller using information received by another controller. Unknown devices are resolved by selecting devices known to multiple controllers as cross-reference objects, determining sets of possible placements for an unresolved device, and finding one possible placement common to each set. Preferably, the network analyzer is part of a larger distributed storage management program which supports management of storage networks connected to multiple host computer systems through one or more controllers in each respective host, the distributed management program comprising a central manager and a separate agent in each host, the analyzer being part of the agent.

Abstract: An agent receives requests containing multiple parameters over an information processing network. The process of obtaining information responsive to the request varies depending on the values of the parameters. The agent constructs a hash key using the parameter values, and uses the hash key to index an entry in a hash function table, the entry having a set of parameter values and a pointer corresponding to the function used to service a request for the indicated parameter values. The agent uses the pointer to call the function to service the request Preferably, the parameters may include wild cards, which are expanded into multiple requests, from which multiple hash keys are derived and multiple functions are called. The agent is preferably part of a larger distributed storage management program, comprising a central manager and a separate agent in each of multiple host computer systems.

Abstract: A distributed storage management program manages a network comprising multiple data storage devices attached to multiple host computer systems. The management program includes a separate agent in each host, and a central manager. The agents gather data and communicate with the manager across a communications path which is independent of the storage network. The manager collates the data from different agents to produce a coherent view of the network. Preferably, each local agent actively builds an internal topological view of the network as seen by its host and collects data such as error events, which it stores in internal data structures. The manager is able to resolve gaps in the information of each agent from information provided by other agents. Preferably, the manager represents the network as a collection of objects of different classes in an object-oriented class library. This collection is graphically displayed in a logical and understandable manner to a user on a display device.