International Business Machines Corporation

Mien Shih

Juan Li

Paul Hodges

Dung Kim Nguyen

Hai-Fang Yun

Michael Garwood Hurley

Norman Kenneth Ouchi

A data processing system having multiple independent paths for communication between a host and a plurality of storage devices where each path has its own queue for servicing requests generated by the host for accessing the storage devices. Each request is assigned a unique sequential ID before it is stored, along with its unique ID, in all the queues. Each storage device has a 'mailbox' register where the ID and the status of the latest request being carried out is stored. Queues are serviced and their status updated based on the content of the mailbox in each storage device. The combination of assigning a unique task ID to each request and a 'mailbox' register in each storage device allows the queue in each path to be completely out of sync with each of the queues in the other paths without causing data integrity problems, duplication of requests at the device level, or a need for complex locking schemes to keep the queues in sync with each other.

Multipath I/O storage systems with multiipath I/O request mechanisms

In a storage system comprising an array of storage devices including a processor and memory, a plurality of data blocks are organized on the storage devices in segments striped across the storage devices. A main directory, stored in memory, contains the location on the storage device of each of the data blocks. For each segment a segment directory having information on the data blocks in the segment is stored on the storage devices. When a damaged segment directory is detected, a checkpoint of the main directory is written to the storage devices. A list is maintained of damaged segment directories such that segments on the damaged segment directories list are not garbage collected. Following a main directory recovery procedure, the damaged segment directories are reconstructed using the main directory.

System and method for recovering a segment directory for a log

In a storage system comprising an array of storage devices including a processor and memory, a plurality of data blocks are organized on the storage devices in segments striped across the storage devices. A main directory stored in memory contains the location on the storage device of each of the current data blocks. A method is provided for recovering a main directory in the event that the main directory becomes damaged. A segment directory having information on the data blocks in the segment is stored as part of the segment on the storage devices. Periodically a checkpoint of the main directory is written to the storage devices. A list is maintained of closed segments written to the storage devices since the checkpoint directory was written to the storage devices. During a main directory recovery procedure, the checkpoint of the main directory is read into memory, and for each segment that is indicated by the closed segments list as having been closed since the checkpoint of the main directory was written to the disk, the information in the corresponding segment directory is used to update the checkpoint directory.

System and method for recovering a directory for a log structured array

Multipath I/O storage systems with multipath I/O request mechanisms

Growing community of inventors

Saratoga, CA, United States of America

Mien Shih