Lecture 11 (unfinished) Flashcards
What are the 6 disk scheduling algorithms
First Come First Served (FCFS) Shortest Seek Time First (SSTF) SCAN Circular SCAN (CSCAN) LOOK CLOOK
Storage Techniques in HPC:
DAS
Direct Attached Storage (DAS): Drives are installed
physically in the box
Storage Techniques in HPC:
NAS
Network Attached Storage (NAS): Storage is not
installed physically but reachable via a TCP/IP
network.
File-level access
Storage Techniques in HPC:
SAN
Storage Area Network (SAN): A distributed cluster of
storage. Needs a specific Storage-Specific switch
(typically Fiber- switch)
Block-level access
What is file-level access?
Easy to implement
Stores data in files and folders
Less Expensive
Suitable for mass storage
What is block level access
Better performance
Can treat each block as an independent disk
More reliable
Can support external boot-up over network
What does RAID stand for?
RAID : Redundant Array of Independent Disks
Software RAID vs Hardware RAID
Software:
- Lower cost
- Support of disk duplexing
Hardware:
- Faster and more reliable
- Processing load in on the dedicated controller, not on the OS
What is RAID 0 (disk-striping )
- 2 disks needed
- Does not support Fault Tolerance (FT)
- Only supports load balancing in both read and write
- 100% Capacity
What is RAID 1 (disk-mirroring)
• 2 disks or even number of disks needed
• Supports FT by mirroring primary disk to the backup
one.
• 50% utilization
What is RAID 5 (Disk-striping with parity)
• 3 disks needed
• Data is stripped into primary disk and backup is stored as parity bits
• Uses Hamming Code for Error Correction
• More complex in utilization, typically needs dedicated
RAID controller
• 1/n Capacity loss
• More expensive than RAID 1
What is RAID 6 ()
• Similar to RAID5 but with a backup parity to
support extremely high availability
• 2/n Capacity loss
What is RAID 10
• Striping (RAID 0) + Mirroring (RAID 1)
What are files?
Data collections created by users
What are 3 Desirable properties of files:
Long-term existence
Files are stored on disk or other secondary storage and do not disappear when a user logs off
Shareable between processes
Files have names and can have associated access permissions that permit controlled sharing
Structure Structure
Files can be organized into hierarchical or more complex structure to reflect the relationships
among files
What does the file management system do?
Meet the data management needs of the user
Guarantee that the data in the file are valid
Optimize performance
Provide I/O support for a variety of storage device types
What are file systems?
Is a Data structure located into RAM by the OS and is used to access storage elements
Provide a means to store data organized as files as well as a collection of functions that can be performed on files
What are the four terms commonly used when discussing files?
Field
Record
File
Database
What is a Field?
Basic element of data
Contains a single value
What is a File?
Collection of similar records
Treated as a single entity
What is a Database?
Collection of related data
Relationships among elements of data are explicit
What is a Record?
Collection of related fields that can be treated as a unit by some application program
What is Logical I/O?
Enables users and applications to access records
Provides general-purpose record I/O capability
Maintains basic data about file
What are the 5 different file organization types?
Pile Sequential Indexed sequential Indexed Hashed
What is a Direct/Hashed file?
Access directly any block of a known address
Makes use of hashing on the key value
Where is a hashed file used?
Often used where:
Very rapid access is required
Fixed-length records are used
Records are always accessed one at a time
2 examples of Hashed file?
Directories
Pricing tables
What are the typical operations of a file system?
Typical operations include: Create Delete Open Close Read Write
What are the types of operations performed on a directory?
Search Create files Delete files List directory Update directory
What are the 2 issues that arise with file sharing?
Access rights
Management of simultaneous access
