1. Database Management System
Lecture - 34
© Virtual University of Pakistan

2. © Virtual University of Pakistan
Data Storage Concepts
© Virtual University of Pakistan

3. Classification of Physical Storage Media
Media are classified according to three characteristics
Speed of access
Cost per unit of data
Reliability
© Virtual University of Pakistan

4. Classification of Physical Storage Media
We can also differentiate storage as either
volatile storage
non-volatile storage
© Virtual University of Pakistan

5. Physical Storage Media
Typical media available are:
Cache
Main memory
Flash Memory
© Virtual University of Pakistan

6. Physical Storage Media
Magnetic disk
Optical storage (CD or DVD)
Tape storage
© Virtual University of Pakistan

7. © Virtual University of Pakistan
Memory Hierarchy
CACHE
MAIN MEMORY
FLASH MEMORY
MAGNETIC DISK
OPTICAL DISK
MAGNETIC TAPES
© Virtual University of Pakistan

8. RAID – Redundant Array of Inexpensive Disks
Many disk that look as a single disk to OS but have better performance and better reliability.
© Virtual University of Pakistan

9. © Virtual University of Pakistan
RAID
RAID have the property that the data are distributed over the drives to allow parallel operations.
© Virtual University of Pakistan

10. © Virtual University of Pakistan
RAID 0
Simple Striping
Virtual single disk is divided up into strips of k sectors each.
RAID 0 writes consecutive stripes over the drives in round robin fashion.
© Virtual University of Pakistan

11. RAID 0 1 5 9 2 6 10 3 7 11 4 8 12
Note: This example is a basic virtual drive where
each element depicted as a disk is a physical disk
© Virtual University of Pakistan

12. © Virtual University of Pakistan
RAID 0
Controller will break any disk command into k commands (one for ech of the disks) and will read/write in parallel.
© Virtual University of Pakistan

13. © Virtual University of Pakistan
RAID 1
It duplicates all the disks.
On write, every stripe is written twice. On a read, either copy can be used.
© Virtual University of Pakistan

14. © Virtual University of Pakistan
RAID 1
Fault tolerance is excellent: if a drive crashes, the copy from the duplicated disk is simply used instead.
© Virtual University of Pakistan

15. RAID 1 -Simple Mirroring2 3 1’ 2’ 3’
© Virtual University of Pakistan

16. © Virtual University of Pakistan
RAID 1 Multi-Mirroring
Three copies of all data 1 2 3 1’ 2’ 3’
1’’
2’’
3’’
© Virtual University of Pakistan

17. © Virtual University of Pakistan
RAID 2-3
For reliability simple parity check code is used.
Parity bit is stored on separate disk.
© Virtual University of Pakistan

18. © Virtual University of Pakistan
RAID 3
Can correct single error.
If a drive crashes, the controller just consider all its bits as 0.
© Virtual University of Pakistan

19. © Virtual University of Pakistan
RAID 3
If no parity error, its bit is considered 0. If parity error, its bit is considered 1.
Huge load of the parity disk.
© Virtual University of Pakistan

20. © Virtual University of Pakistan
RAID 4
RAID 4 works with stripe again.
Stripe-to-stripe parity written onto a extra drive.
© Virtual University of Pakistan

21. © Virtual University of Pakistan
RAID 4
If each stripe is k bytes long, all the strips are EXORed together, resulting in a parity strip stored on parity disk
© Virtual University of Pakistan

22. RAID 3 or RAID 4 – Non-Rotating Parity 0
Fixed parity on the first element of the virtual drive P 1 5 9 2 6 10 3 7 11 4 8 12
© Virtual University of Pakistan

23. © Virtual University of Pakistan
RAID 5
Eliminates the bottleneck of the heavy load on the parity drive by distributing the parity bits uniformly over all drives.
© Virtual University of Pakistan

24. © Virtual University of Pakistan
RAID 5
Rotating Parity 0 with Data Restart
Parity starts on the first element of the virtual drive
© Virtual University of Pakistan

25. © Virtual University of Pakistan
RAID 5 P 5 9 1 P 10 2 6 P 3 7 11 4 8 12
© Virtual University of Pakistan

26. © Virtual University of Pakistan
File Organization
The manner data records are stored and retrieved on physical devices
The technique used to find and retrieve store records are called access methods.
© Virtual University of Pakistan

27. Sequential File Organization
Records are arranged on storage devices in some sequence based on the value of some field, called sequence field.
© Virtual University of Pakistan

28. Sequential File Organization
Sequence field is often the key field that identifies the record.
Simple, easy to understand and manage, best for providing sequential access.
© Virtual University of Pakistan

29. Sequential File Organization
Not feasible for direct or random access, inserting/deleting a record in/from the middle of the sequence involves cumbersome record searches and rewriting of the file.
© Virtual University of Pakistan

30. Sequential File Organization- not shown
STUDENT
stId
stName
prName
cgpa
S1020
Sohail Dar
MCS
2.8
S1014
Shoaib Ali
BCS
2.78
S1028
Tahira Ejaz
3.2
S1034 …
S1048
© Virtual University of Pakistan

31. Database Management System
Lecture - 34
© Virtual University of Pakistan