1. File Processing : Storage Media
2018, Spring
Pusan National University
Ki-Joune Li

2. Major Functions of Computer
Computation
Storage
Communication
Presentation

3. Storage of Data Major Challenges
How to store and manage a large amount of data
Example : more than 100 peta bytes for EOS Project
How to represent sophisticated data

4. Modeling and Representation of Real World
Example
Building DB about Korean History
Very complicated and Depending on viewpoint
Database Course : 2017 Fall semester
Real World
Computer World

5. Managing Large Volume of Data
Cost for Storage Media
Not very important and negligible
Processing Time
Time is the most valuable resource
Comparison between main memory and disk access time
RAM (Random Access Memory) : several 10-9 sec
SSD (Solid State Driver) : under sec
HDD (Hard Disk Driver): several 10-3 sec
 HDD is 106 times slower than RAM
Difference between handling data in RAM and HDD
Handling data in HDD: Same way that we handle data in RAM
How to handle this gap between RAM and Disk Memory

6. Managing Large Volume of Data
Management of Data
Secure Management
From hacking
From any kinds of disasters
Consistency of Data
Example
Failure during a flight reservation transaction
Concurrent transaction

7. Goals of File Systems To provide with
1. efficient Data Structures for storing large and complex data
2. Access Methods for rapid search
3. Query Processing Methods
4. Robust Management of Transactions

8. Memory Hierarchy Large Data Volume Memory Hierarchy
Not be stored in main memory
But in secondary memory
Memory Hierarchy
Faster
Cache Memory
8 M bytes (Core i7, L3 Cache)
Cheaper
Main Memory
16 G bytes
Secondary Memory
1 T bytes
Tertiary Memory
10 Peta bytes

9. SSD (Flash Memory) Solid State Driver
Only Electronic Operations unlike HDD.
Characteristics
Aging Problem: only a limited number of write/erase cycles. (e.g. 1 M)
Asymmetric Read/Write Speed:
a byte (or word) can be read at a time
Write: Erasing of memory has to be done to an entire bank of memory
Reading is fast and a byte (or word) can be read at a time
Writing is a little bit slower than reading
Easing is slower
NAND vs. NOR Flash Memory

10. Optical Storage Non-volatile Speed Juke-box systems CD, DVD
Slower than HDD
Juke-box systems
Large numbers of removable disks,
Few drives, and
Mechanism for automatic loading/unloading of disks
For storing large volumes of data

11. Tape Non-Volatile and Large Volume (e.g. 15 TB per Cartridge)
Primarily Used for backup
Sequential access: much slower than disk
But data transfer rate: up to 750 MB for some tape driver

12. Data Access with Secondary Memory
Get Data
Hit Ratio rh = nh / na
Access Request
Get Data
How to increase hit ratio ?
If in main memory
Main Memory
Load on main memory
Access to Disk
If not in main memory
Disk

13. Why Hit Ratio is so important ?
Example
for(int i=0;i<1000;i++)
Nbytes=read(fd,buf,100);
1000 disk accesses ?
when rh = 0
when rh = 1
1000 * 10-2 sec = 10 sec
1000 * 10-8 sec = 10-5 sec

14. Physical Structure of Disk
200~400 sectors
512 bytes
2 * nDF

15. Disk Access Time Disk Access Time t = tS + tR + tT , where
tS : Seek Time
Time to reposition the head over the correct track
Average seek time is 1/2 the worst case seek time
4 to 10 milliseconds on typical disks
tR : Rotational Latency
Time to reposition the head over the correct sector
Average rotational latency : ½ r (to find index point) + ½ r = r
In case of rpm : r =1*60sec/15000 = 4 msec
tT : Transfer Time
Time to transfer data from disk to main memory via channel
Proportional to the number of sectors to read
Real transfer time is negligible

16. Block-Oriented Disk Access
Example
for(int i=0;i<1000;i++)
Nbytes=read(fd,buf,10);
10 bytes
1000 times
100 times
Buffer in main memory
1024 bytes
Number of Disk Accesses
10 times
1 block (e.g bytes)

17. Disk Block Unit of Disk Access Block Size Why not large block ?
Normally multiple of sectors
1K, 4K, 16K or 64K bytes depending on configuration
Why not large block ?
Limited by the size of available main memory
Too large : unnecessary accesses of sectors
e.g. only 100 bytes, when block size is given as 64K
1 block : 128 sectors (about ½ track, ½ rotation, 2 msec)
Too wasteful