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Method and System for Providing Virtual Defragmentation of Extremely Large Volumes

IP.com Disclosure Number: IPCOM000235456D
Publication Date: 2014-Feb-28
Document File: 2 page(s) / 89K

Publishing Venue

The IP.com Prior Art Database

Abstract

A method and system is disclosed for providing defragmentation of extremely large volumes such that those data sets that were allocated in physical extent units would not have to be actually moved. The method and system disclosed herein modifies the hardware mapping of the physical extents to logical cylinder address on the host system to make it appear that the blocks had actually been moved, without actually moving the blocks.

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Method and System for Providing Virtual Defragmentation of Extremely Large Volumes

Usually, volumes on z/OS have logical tracks and cylinders which correspond to physical mapping of Distributed Data Management (DDM). Even though the z/OS mapping is purely logical, there are still performance and usability reasons that require users to defragment volumes. Current defragmentation methods move data from one logical location to another. A better

methodology is to simply change the physical DDM extent mappings to the corresponding logical tracks and cylinders. This would eliminate the need for the host operating system to issue I/O requests to move extents around on the volume. One reason why this has not been implemented on Home Area (HA) architecture is that the HA physical extent is currently 1GB, or 1113 cylinders. In order to change the mapping, the units that could be remapped would be limited to 1113 cylinders at a time. Moreover, prior to Extended Addressable Volumes (EAV), most data sets were allocated in unit sizes that were smaller than this amount. However,

with EAV support extremely large volumes are now possible, and large data sets can be allocated in 1113 cylinder units or in multiples of 1113 cylinder units.

The method and system disclosed herein provides defragmentation of extremely large volumes such that the data sets that were allocated in physical extent units would not have to be actually moved.

In an exemplary embodiment, the method and system rounds off large allocations on EAV volumes to be in 1GB units, so that the logical allocation units match the physical extent unit. The disclosed method and system modifies the hardware mapping of the physical extents to logical cylinder address on the host system to make it appear that the blocks had actually been moved, without

actually moving the blocks. The method and system swaps the location of the physical extent with a different physical extent in the host's view of the current physical extent. Subsequently, the host data sets that contain location information of data sets, such as the Volume Table Of Contents (VTOC) are updated with the new logical location of the extents. Thereafter, the method and system reduces the overhead of defragmentation for extremely large amount of data on the EAV volumes by restricting the movement of the data sets that were allocated in physical extent units.

The method and system disclosed herein allows users to specify the data class in case the users want a particular data set to use allocation units that match the physical extent size. The data class disclosed above requires the users to have a storage group

with the same setting, so that allocation units of 1113 cylinders are kept available that match the starting location of the physical extent. Thus, when a data set is created with these settings, the extent is set to a multiple of the physical extent size and allocated at the beginning of a physical extent.

In case the users...