One of Marco Linux learning notes

1. When executing scripts, you can use./or. ./(dot space dot slash) to execute script

The./means that another shell is started to execute the script (another process), so when a slash executes the script, the environment variables set will end with the process exiting, where the environment variable settings do not work for the current shell.

. ./equivalent to source./execute the script, source is the command in the execution script, that is, the command is executed in the current process, so the setting of the environment variable in it will affect the current shell.

2. Read the files on the hard drive

Reading the file on the hard disk first to read the file into memory, and then to the memory address to the process, so that the process can read the file.

3.Raid (redundant Arrays of inexpensive Disks, inexpensive redundant disk array)----> (redundant Arrays of independent Disks, independent redundant disk array)

Combining multiple disks as a disk is a technique called raid. The speed and volume of storage is large, but each disk is prone to bad, so the probability of his damage goes up.

In order to prevent change, just a copy of the data two copies, this technology is mirrored mirror. Another technique is the cyclic redundancy check code (RAID4), which is not used to store data on the disk, but the check code on this disk, when one of the bad, the use of checksums and other disk data to recover the data on the broken disk, so that the disk utilization is good, But a two-piece hard drive would have been a terrible break. A rich enterprise, two technology combined.

Because each disk reads to read the checksum disk, he may become a bottleneck for disk reads. So take turns as a check pad--RAID5

raid0--Strip Technology

raid1--Mirroring Technology

4. Neither looking at speed nor focusing on safety, it is a large volume of disk--jbod technology that is composed of many small disks.

5. The interface of the hard drive is: IDE (ATA) (133Mbps), SATA (Serial ATA, Serial ATA) (6Gbps), USB,SCSI (ultrascsi,320mbps)

6. Hardware RAID, software raid

7.BIOS

8. Virtualization

Simulating hardware with software

9.md:meta Device

Dm:device Mapper Logic Device