# How IBM's Storage Controllers Keep Data Backups in the Right Order > A method for storage controllers to track and sequence data updates in a specific order, ensuring that remote backups remain consistent with the original data during a system failure. - **Patent:** US 5682513 - **Original title:** Cache queue entry linking for DASD record updates - **Owner:** International Business Machines Corp - **Granted:** 1997 - **Status:** Public domain (expired) - **Times cited:** 145 - **Field:** telecommunications, semiconductors, mechanical ## What it does This patent describes a way for a storage controller to manage updates to data stored on a disk. When an application updates multiple records, the controller creates a circular queue to track these changes. Each update is linked to the previous one in a backward chain, and a counter keeps track of how many updates are pending. This allows a data mover to read the updates in the exact order they occurred, which is critical for sending them to a remote site for disaster recovery without data corruption. ## What it does NOT cover - Does not cover data storage systems that lack a cache-based circular queue structure. - Does not cover methods of data transmission that do not require sequence-consistent ordering. - Does not cover the specific hardware architecture of the host processor itself. - Does not cover real-time data replication that occurs without a staging queue. ## The clever bit By using a backward-linked chain within a circular queue, the system can efficiently track the sequence of updates without needing to constantly re-sort or re-index the entire list of changes as they arrive. ## Real-world examples 1. Enterprise storage area networks (SAN) 2. IBM z/OS remote copy services 3. Disaster recovery replication software 4. High-availability database transaction logs ## Why it matters This technology is a foundational piece of enterprise disaster recovery. It ensures that if a primary data center fails, the remote backup site has an identical, chronological history of data changes. This prevents 'data skew' where a backup might reflect a later state of one file but an earlier state of another, which would crash databases. ## Frequently asked questions ### What does How IBM's Storage Controllers Keep Data Backups in the Right Order cover? A method for storage controllers to track and sequence data updates in a specific order, ensuring that remote backups remain consistent with the original data during a system failure. ### Who owns patent US 5682513? International Business Machines Corp owns this patent, granted in 1997. ### When does this patent expire? This patent has expired and is now in the public domain — anyone can use the invention freely. ### What is patent US 5682513 cited by? This patent has been cited by 145 later patents that build on its ideas. ### What problem does this patent solve? This technology is a foundational piece of enterprise disaster recovery. It ensures that if a primary data center fails, the remote backup site has an identical, chronological history of data changes. This prevents 'data skew' where a backup might reflect a later state of one file but an earlier state of another, which would crash databases. ### What does this patent NOT cover? Does not cover data storage systems that lack a cache-based circular queue structure. **Full plain-English explainer:** https://patentbrief.org/patent/us/5682513/cache-queue-entry-linking-for-dasd-record-updates **Original patent:** https://patents.google.com/patent/US5682513 --- _Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._ ## Related patents Semantically similar inventions in the PatentBrief corpus: - [How to Keep Backup Data in the Correct Order](https://patentbrief.org/patent/us/9811430/aws-codepipeline) — A method for ensuring that backup data arrives at a secondary storage location in the exact same sequence it was created at the primary location to prevent data corruption. - [How to Keep Data Safe During a Site Failover](https://patentbrief.org/patent/us/9672117/aws-codedeploy) — A method for keeping data backups synchronized and accessible even when a primary data center goes offline and systems must switch to a backup location. - [How to Send Data Streams Independently Without Connection Overload](https://patentbrief.org/patent/us/7904576/reliable-datagram-via-independent-source-destination-resources) — A method for sending multiple streams of data between devices using independent, reliable paths that keep data in the correct order without needing a constant connection. - [How Virtual Machines Keep Their Data Separate on Shared Storage](https://patentbrief.org/patent/us/9760393/azure-machine-learning) — A method for virtual machines to store data in isolated, non-mixed logical storage units to improve security and management efficiency within a shared physical storage pool. - [How Microsoft Organizes Data in Multi-Tier Storage Systems](https://patentbrief.org/patent/us/9824092/file-storage-system-including-tiers) — A method for organizing computer data into three specific tiers—log, hash, and journal stores—to make writing and reading data faster and more efficient.