INTELLIGENT DISK SUBSYSTEM OVERVIEW
Introduction:
This system optimize all available storage solution automaticallyData must be automatically placed and stripped across multiple physical storage resources, including arrays, RAID groups, Disk types and Controllers.
Four main components:
- Front End
- Cache
- Back End
- Physical Disk
Front End:
Interface between host and storage system.
Consist of two components
- Front End Ports: enable host to connect to intelligent subsystem
- Front End Controllers: is used for routing data from cache using internal bus.
Uses command queueing algorithm for I/O processing.
Cache:
Improves performance
Made up of semiconductor memory.
Holds data for temporary purpose to reduce time required to service I/O request from host.
Structure of cache:
- Organized into pages
- Consist of data store and TAG RAM.
- Track of each address line is recorded via Tag RAM
Read Operation:
- Host sends read request, front end controllers search tag ram to determine required data is available in cache.
- Cache hit data is found on cache while cache miss data is not found in cache but in main memory.
- In case of miss read policies are:
- Read through
- No read through
Write Operation:
Policies are:
- Write through cache
- Write back cache
Back End:
1. Interface between physical disk and cache
2. Controls data transfer
3. Two components:
- Back end ports
- Back end Controllers
Physical disk:
1. It stores data persistently.
2. Disks are connected to back end with either SCSI or a fibre channel.
3. Logical Unit Numbers(LUN) are used for identifying virtual hard disk patterns.