Shulou(Shulou.com)06/02 Report--

Preface

What is a disk quota? What is the use of disk quotas?

A disk quota is a quota that an administrator can impose on the disk space available to each user in this domain, that is, each user can only use disk space within the maximum quota range. Disk quotas monitor the use of individual user volumes, so each user's utilization of disk space does not affect the disk quotas of other users on the same volume. Disk quotas have the following characteristics:

Disk quotas can track and control the disk usage of each user. This tracking is achieved using the ownership of a file or folder. When a user copies or stores a new file on the Linux ext 2 ramp 3 partition, he has ownership of the file, and the disk quota program counts the size of the file into the user's disk quota space.

When the disk quota is set, the remaining space in the partition report actually refers to the remaining space within the current user's disk quota range. The disk quota program tracks and controls disk usage for each partition independently, regardless of whether they are on the same physical disk or not.

To achieve disk quotas, use the following steps:

Check to see if the Linux kernel turns on disk quota support. Modify / etc/fstab to activate the quota option for the selected file system. Update the mount file system for the changes to take effect. The aquota.user file is created when the file system boots. Scan the corresponding file system and use the quotacheck command to generate a basic quota file. Use the edquota command to impose quota limits on specific users. Finally, activate the quota with the command.

Disk array RAID

Disk array is referred to as RAID (Redundant Arrays of Inexpensive Disks,RAID), which means "cheap and redundant disk array". The principle is to use array to make disk group, and cooperate with the design of scattered arrangement of data to improve the security of data. Disk array is mainly aimed at hard disk, in terms of capacity and speed, it can not keep up with the development of CPU and memory. Disk array is composed of many cheap, small, stable and slow disks into a large disk group, using the addition effect produced by individual disks to provide data to improve the performance of the whole disk system. At the same time, when storing the data, we use this technology to cut the data into many sections and store them on each hard disk.

The disk array can also make use of the concept of Parity Check, when any hard disk in the array fails, the data can still be read out, and when the data is reconstructed, the data in the failed hard disk will be rebuilt into the new hard disk after calculation.

Disk quota management

(1) conditions for realizing disk quota

Linux kernel support is required

Install xfsprogs and quota software packages

(2) characteristics of Linux disk quota

Scope: for the specified file system (partition)

Restricted object: user account and group account

Type of limit: disk capacity, number of files

Limit method: soft limit, hard limit

Attention!

(1) restrict user accounts and group accounts. Soft limit is less than or equal to hard limit.

(2) most of the command settings are temporary and the restart fails. The profile settings are permanent.

I. the process of disk quota

1. Mount the file system in a way that supports quota.

2. Edit quota settings for user and group accounts

3. Verify the disk quota function

4. View disk quota usage

RAID disk array

RAID is the abbreviation of Redundant Array of Independent Disksde in English and independent redundant disk array in Chinese. RAID combines multiple independent physical disks in different ways to form a hard disk group (logical hard disk), which provides higher storage performance and data backup technology than a single hard disk. The different ways to form a disk array are called RAID levels, and the commonly used RAID levels are as follows: RAID0, RAID1, RAID5, RAID6, RAID1+0, etc.

0

RAID0 continuously separates data in bits or bytes and reads / writes in parallel on multiple disks, so it has a high data transfer rate, but it has no data redundancy, so it is not a true RAID structure. RAID0 simply improves performance and does not provide a guarantee for data reliability, and one of the disk failures will affect that many data RAID0 cannot be used in situations with high data security requirements.

RAID1 achieves data redundancy through disk data mirroring, and then generates backup data on pairs of independent disks. When the original data is busy, the data can be read directly from the mirror copy, so RAID1 can improve read performance. RAID1 has the highest unit cost in the disk array, but provides high data security and availability. When a disk fails, the system can automatically switch to the mirrored disk to read and write without the need to reorganize the failed data.

RAID5N (N > = 3) block disk is composed of an array. One piece of data produces a stripe, and at the same time, there is a check data. A total of N pieces of data are cyclically stored on N block disks to read and write at the same time. The read and write performance is very high, but due to the problem of verification mechanism, the write performance is relatively low (Nmur1) / N capacity reliability is high, allowing one disk to be broken, and does not affect all data.

RAID6N (N > = 4) blocks form an array. Compared with RAID5, a second independent parity information block is added to the (NMUI 2) / N capacity. Two independent parity systems use different algorithms, even if two disks fail at the same time, it will not affect the write loss of data use compared with RAID5, so the write performance is poor.

RAID 1: 0

After the image of N (even number, N > = 4) block is pairwise, a RAID0N/2 capacity NCPU 2 disk is formed to write at the same time. The N block disk has high reading performance and high reliability.

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