Virtual Tape Storage Partial Recall via Physical Block ID
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Solution Overview
Problem
Virtual tape storage (VTS) systems employing hierarchical storage face inefficiencies in recall operations due to the need to retrieve entire logical volumes, leading to increased wait times for users, especially with larger logical volumes, and the lack of direct positioning information for physical tape media.
Innovation Solution
A VTS system that determines a physical block ID (PBID) based on the starting logical block ID (SLBID), compression ratio, and data record size to access only the required portion of a logical volume, allowing for partial volume recall and reducing the need to copy entire logical volumes into cache.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire logical volume is copied from tape to cache, then the data retrieval is guaranteed to be complete, but the data retrieval time increases significantly and system efficiency decreases
Solution Approach 1:
The patent extracts only the specific physical blocks containing the requested logical blocks from the tape medium, rather than copying the entire logical volume. The system calculates the starting physical block ID based on the requested logical block ID and compression ratio, then selectively retrieves only the necessary data portions, eliminating unnecessary data transfer time while ensuring complete retrieval of requested data
Solution Approach 2:
The patent implements partial action by retrieving exactly the portion of data needed (the specific physical blocks containing requested logical blocks) rather than the excessive action of copying the entire logical volume. This partial retrieval approach maintains reliability for the requested data while significantly reducing the time and resources consumed by the retrieval operation
2Speed
If native tape drives are added to replace non-native ones, then the data retrieval speed improves, but the system cost increases significantly
Solution Approach 1:
The patent changes the operational parameters of the existing VTS system by implementing selective physical block retrieval based on calculated starting positions and compression ratios. This parameter change enables faster data retrieval without requiring hardware changes, as the system optimizes the data retrieval process through intelligent calculation and selective copying rather than through faster native tape drives
Solution Approach 2:
The patent uses a virtual copy approach where the system creates a selective copy of only the necessary physical blocks from tape to cache based on logical block requests. This virtual copying mechanism provides fast access to specific data portions without requiring physical native tape drives, maintaining system cost-effectiveness while improving retrieval speed for hierarchical storage workloads
3Measurement precision
If the starting physical block ID is calculated based on compression ratio and logical block ID, then the precise positioning on tape is achieved, but the calculation complexity increases
Solution Approach 1:
The patent performs preliminary action by calculating the starting physical block ID in advance based on the requested logical block ID and the compression ratio stored in the volume descriptor. This pre-calculation enables direct positioning on the tape medium without requiring sequential searching or scanning, achieving precise positioning while the calculation complexity is minimized through using pre-stored compression ratio information
Data Source
AI summary
According to one embodiment, a computer program product includes a computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising: computer readable program code configured to receive a mount request to access at least one host data record on a virtual tape storage (VTS) system; computer readable program code configured to determine a number of host compressed data records per physical block on a magnetic tape medium; computer readable program code configured to determine a physical block ID (PBID) that corresponds to the requested at least one host data record; computer readable program code configured to access a physical block on the magnetic tape medium corresponding to the PBID; and computer readable program code configured to output the physical block without outputting an entire logical volume from the magnetic tape medium that the physical block is stored to. Other systems and computer program products are also described.