Linux-ln-raid

Hard Links

LN is created. as follows, create a hard link to the file oldfile.

Link Oldfile newfile

ln Oldfile NewFile

Because a hard link is a file with the same inode number with only a different file name, hard links have the following characteristics:

The file has the same inode and data block;

Only files that already exist can be created;

Cannot cross file system for hard link creation;

The directory cannot be created, only the file can be created;

Deleting a hard-link file does not affect other files that have the same inode number.

Soft links

Ln-s Oldfile Newfil

A soft link differs from a hard link in that the file is a soft connection if the contents of the file's user data block are pointing to the path name of another file.

Soft link is a normal file, but the content of the data block is a bit special. Soft links have their own inode numbers and user data blocks . Therefore, the creation and use of soft links does not have many restrictions similar to hard links:

Soft links have their own file attributes and permissions, etc.;

You can create a soft link to a nonexistent file or directory;

Soft link can cross file system;

Soft links can be created on files or directories;

When you create a soft link, the link count i_nlink not increase;

Deleting a soft link does not affect the file being pointed to, but if the original file being pointed to is deleted, the associated soft connection is called a dead link (that is, dangling link, if it is re-created by pointing to the path file, the dead link can revert to the normal soft link).

Raid:

Redundant arrays of inexpensive disks low-cost disk array

Independent Standalone disk array

BERKELEY:A case for redundant arrays of inexpensive disks

Hard raid: Some controllers have CPU, memory, battery.

Soft raid:

Levels: Level

Raid0

Raid1

Raid2

...

Raid5

Raid6

Raid10

Raid01

Raid4: At least three blocks. Two pieces of data, a piece of check code. Implemented by XOR or operation

Implementation of software RAID on CENTOS6

Combined with MD (multi devices) in the kernel

Mdadm-c dev/md0-a yes-n 3-x 1-l 5/dev/sda{7,8,9,10} three disc RAID5, piece of spare

-D Display RAID details

Mdadm-d/dev/md0

Management mode

-F: Mark the specified disk as damaged

-R: Remove disk

-A: Adding disks

Observing the state of MD

Cat/proc/mdstat

Stop MD Device

Mdadm-s/dev/md0

Watch-n1 ' Cat/proc/mdstat ' not a second refresh view

Linux-ln-raid