Date: Jan 07, 1993 X3T9.2/93-003 rev 0 To: X3T9.2 Committee (SCSI) From: George Penokie (IBM) Subject: SCSI Disk Array Model 1.0 Glossary 1. Check Data Mapping - The distribution of the check data within a set. 1. Data Mapping - The distribution of data within a set. 1. Mapping - The distribution of data and check data (if any) within a set. 1. Set - A group of devices which have a single mapping behavior. Sets are independent from one another. 2.0 Model for SCSI disk arrays The following is a model which defines the behavior of SCSI disk arrays. It is not intended to define any requirements nor is it intended to alter any requirements defined elsewhere in this standard. 3.0 Behavioral Control A SCSI disk arrays behavior may be controlled from different levels within a system. Listed below are examples of three levels of control which may exist within a system. Software Disk Array - The OS is in control of the array and is responsible for configuration and data reliability. Transparent Disk Array - The OS has no knowledge of the array during normal operations and is not responsible for data reliability. The array characteristics and statistical information are available through maintenance software. Hybrid Disk Array - The OS is aware of the array and is responsible for the initial configuration but not the data reliability. The OS is notified of exception conditions so that a corrective action can be indicated. Date: Jan 07, 1993 X3T9.2/93-003 rev 0 4.0 SCSI Disk Array Configuration 4.1 Configuration Requests A SCSI disk arrays configuration is initialized and controlled by configuration requests. Configuration requests define the: -Number of addressable devices within a set. -LBA range within a set. -Capacity within a set. -Expansions to a set. -Contractions to a set. -Data mapping within a set. (Note: Data mapping may allow data to be duplicated) -Check data mapping within a set. 4.2 Reconstruction Requests A SCSI disk arrays reconstruction is initiated by reconstruction requests. The following are the methods of reconstruction which may be available within a set: -Remapping a range of LBAs or a device into an unused range of LBAs or device. -Reconstruction of a range of LBAs or device(s) using check data information or duplicate data. -Resynchronization of the check data within a set. 4.3 Configuration Control The level within a system which receives configuration requests controls the following behaviors: -Reading data from and writing data to locations based on the mapping in effect for the set being addressed. -Calculates and updates the check data (if any). -Attempts to correct any bad data using check data or duplicate data. -Determines when a device or LBA range should be disabled and/or replaced. -Indicates to a higher level that a failure occurred and how to fix the failure. 5.0 Exception Conditions Exception conditions indicate to a higher level that: -a repair action is requested, -a repair action is required, or -an error occurred. Which exception conditions are indicated and how often they are indicated is based on requests received from a higher level.