Magnetic Disk Controller Defect-Aware Logical Address Allocation
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Solution Overview
Problem
Magnetic disk devices face performance deterioration due to defects like bumps on the disk surface, which cause collisions and increase waiting times, affecting read and write sequential performance.
Innovation Solution
A magnetic disk device and control method that allocates logical addresses differently based on the number of defects, excluding defect areas from the recording zone by using a system controller to manage and allocate addresses, thereby avoiding collisions and optimizing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heaters are used to protrude the reader and writer toward the disk surface to improve read/write characteristics, then the margin for read/write characteristics is secured, but the head may collide with bumps on the disk surface
Solution Approach 1:
The system performs preliminary actions by cooling the head before seeking to a track that may contain bumps, and by advance detection of bump locations through defect information. This allows the head to approach the track in a retracted state, avoiding collision before the bump is encountered.
Solution Approach 2:
The system dynamically adjusts the protrusion state of the head by controlling the heater based on the detected bump location. When a bump is detected in the target track, the head is kept retracted; when no bump is present, the head is protruded to optimize read/write characteristics. This dynamic adaptation resolves the contradiction between maintaining good read/write characteristics and avoiding bump collisions.
2Object-affected harmful factors
If waiting time is increased before and after the head straddles the bump to avoid collision, then collision avoidance is achieved, but data read performance and data write performance deteriorate
Solution Approach 1:
The system performs preliminary detection of bump locations and stores this defect information in advance. When a seek operation is initiated, the system immediately checks whether the target track contains bumps and adjusts the head protrusion state accordingly, eliminating the need for waiting time before and after straddling bumps.
Solution Approach 2:
The system replaces the mechanical waiting approach with an information-based control system. Instead of waiting for the head to pass over bumps and then cooling down, the system uses defect information to proactively control heater activation, determining in advance whether cooling is necessary based on the presence of bumps in the target track.
3Quantity of substance
If the gap between the head and disk is reduced to improve recording density, then recording density increases, but the head becomes more vulnerable to damage from defects on the disk surface
Solution Approach 1:
The system performs preliminary detection and registration of defect locations on the disk surface. When a seek to a track containing defects is required, the system proactively cools the head to retract it before the seek operation, preventing collision with defects. This allows the head to operate at reduced gap distances for high recording density while maintaining durability through advance protective action.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively avoids collisions with defects and suppresses performance deterioration during data read and write operations, even when defects are present, by strategically allocating logical addresses and managing head movements.
Implementation Method 1
The heaters heat the reader and writer to thereby protrude the reader and writer outwardly toward the surface side of the disk
Implementation Method 2
the reader and writer are cooled and, after waiting for the termination of the protrusion, the seek is started
Data Source
AI summary
According to one embodiment, a magnetic disk device comprises magnetic disks, heads, and a controller. The controller does not allocate logical addresses to sectors of a first area to be specified in such a manner as to correspond to a defect existing in a predetermined recording area, the first area being within the predetermined recording area constituted of a plurality of cylinders adjacent to each other in the magnetic disks, and uniquely allocates logical addresses to sectors of a second area other than the first area. The controller makes allocation of logical addresses to the sectors of the second area different from each other according to the number of defects existing in the predetermined recording area.