Learning record 010-disk basics (to be perfected)

I. The role of/DEV/NULL/2>&1

1. Scheduled tasks send a temporary heap of/var/spool/clientmqueue for a long time, resulting in inode reduction, plus >/dev/null/2>&1
2. Two ways to delete a directory:
Cd/var/spool/clientmqueue &&ls |xargs rm-f
Cd/var/spool &&ls |RM-RF Clientmqueue
mkdir clientmqueue &&chmod 770 clientmqueue && chown-r root:root/var/spool/clientmqueue
Related blog: http://oldboy.blog.51cto.com/2561410/1541515

Two. Basics of disk

1. The disk (hard disk) is the data, so you should understand it
1956 IBM shows the world the first disk IBM RAMAC, capacity 5MB
With the development of science and technology, its trend is: small size, fast, large volume, the use of safety
Realized from the following points: High storage density read more sensitive head, spindle speed faster, storage technology to improve
System of Disk:
Empty

2. Structure inside the disk:
Related blog: http://blog.sina.com.cn/s/blog_4f1a5f3c0100hen5.html
A. Disk manufacturers: Western data (Westerndigital) WD200 (Thailand A swollen, the disk must rise)
The disk surface has a vent hole for balancing the air pressure.
Disk afraid of shaking, and dust.
B.free-m look at the disk memory the second row buffers/cache the last digit 798,
[Email protected] dd]# free-m
Total used free shared buffers Cached
mem:988 442 546 0 116 135
-/+ buffers/cache:190 798
swap:1983 0 1983
C.buffers is write buffer, Sync writes buffer buffers data to disk
D.cache reads the cache, the data in the disk is read out and stored in the cache.
E. Disk read data works by using the polarity of a particular magnetic force to record data

3. The interface type of the disk
IDE: Early Home
SCSI: Early Server domain
SATA (serial disk): The popular Home area
SAS: A popular server area (multiple production environments)
Fibre Channel (FC): High-end server
Determine the performance of the disk:
A. Spindle speed
B. Disk interfaces and types
C. Caching

Advantages and disadvantages of 4.SSD solid state drives
A. Quick Start (no acceleration of motor rotation)
B. Fragmentation does not affect read time
C. Fast write speed
D. No noise, low fever, large operating temperature range, small size
E. No mechanical failure (bad recovery), high cost, low capacity, vulnerable (power outage, disk interference), write Data Limited

5. Enterprise-Class SAS HDD:
Common 15000 rpm 300G 600G 1000G
Business servers primarily for external services (online)

6. Enterprise-Class SATA HDD:
Common SATA Hard drives 7200-10000 rpm, 1T 2T
Business servers primarily for internal service delivery (offline)

Learning record 010-disk basics (to be perfected)