Method for Scheduling Writes in a Duplexed DASD Subsystem
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
This article describes a method of scheduling writes in a duplexed direct-access storage device (DASD) subsystem, which dynamically adapts to read and write request rates to improve performance. A well-known technique for providing high availability to data is to store the data on two devices, i.e., to duplex devices. For example, if the repair time for a device failure is one day, if devices are unavailable due to a failure an average of one day a year, if a failure is equally likely on any day, and if failures are independent, then it would be expected that both devices would be unavailable on the same day only once roughly every 365 years. Normally, though, both devices are available.