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Dasd Storage Optimization by Sector Address Scrambling

IP.com Disclosure Number: IPCOM000043090D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Altmann, WC: AUTHOR

Abstract

This article describes a method of connecting all of the unused sectors on a memory medium to appear as one contiguous region and presents a novel approach to accessing data stored as a recorded image on a mass storage medium. The advantage of this approach is in the maximum utilization of physical storage capability with minimal impact to speed and with efficiency of data transmission, by scrambling the addresses of the various stored data storage locations. It thus eliminates the need to physically alter data in memory in order to optimize storage since only the addresses stored in the controller's physical hardware need be updated. In present computer systems both a directory and free list must be maintained for the system to know where to delete and allocate files.

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Dasd Storage Optimization by Sector Address Scrambling

This article describes a method of connecting all of the unused sectors on a memory medium to appear as one contiguous region and presents a novel approach to accessing data stored as a recorded image on a mass storage medium. The advantage of this approach is in the maximum utilization of physical storage capability with minimal impact to speed and with efficiency of data transmission, by scrambling the addresses of the various stored data storage locations. It thus eliminates the need to physically alter data in memory in order to optimize storage since only the addresses stored in the controller's physical hardware need be updated. In present computer systems both a directory and free list must be maintained for the system to know where to delete and allocate files. However, deleting files can create free spaces, and these free spaces to be usable must now be merged together into a single large free area. Until this is done, whereas the total free space may be adequate to allocate a new file, there may be no single area large enough to suit the new file. This article teaches that this merging need not be done if the valid files are rewritten in blocks beginning at one boundary of the address range of the memory medium and continuing through contiguous blocks until the files have been shifted together without, however, moving the actual file data. Thus, the free spaces on the device need not be physically adjacent or in one contiguous region to be useful. The addressing of the valid data is rearranged so that all the free spaces appear to be a physically adjacent unit. Thus, the logical addresses and the physical addresses are rearranged. From the point of view of logical addressing by the computer system the free space forms a single contiguous area. To accomplish this, the logical address sequence (LAS) is adjusted by changing all addresses for physical blocks from the first block of the deleted file up to, but not including, the first block of the free space Each address is adjusted by subtracting the file size of the deleted file from the address of each block of each file after the deleted file in the logical address sequence. Once this is accomplished, the address of each block of the deleted file is adjusted by adding the number of blocks between the last block of the deleted file and the first block of the free space, leaving the addresses of the file blocks preceding the free space file intact. The above solution creates the appearance of contiguous files while allowing them to be physically noncontiguous on the device. It does, however,...