The server data is all gone! Thinking caused by a RAID5 crash

disk array

1 Disk array Introduction

        disk array （Redundant Arrays of Independent Disks,RAID）, Yes “ Redundant array of Independent Disks ” The meaning of .
        Redundant array of independent disks (RAID,redundant array of independent disks) Is to put a lot of cheaper disks , Combine them into a huge disk pack , Use the data provided by individual disks to increase the performance of the whole disk system . Using this technology , Cut data into sections , Stored on each hard disk separately . By putting data on multiple hard disks , I / O operations can overlap in a balanced way , Improved performance . Because multiple hard disks increase the mean time between failures , Storing redundant data also adds fault tolerance .
        Raid can also utilize parity checking (Parity Check) The concept of , When any hard disk in the array fails , Data can still be read out , In data reconstruction , Put the data into the new hard disk after calculation .

2 RAID Disk array classification

There are three types of disk arrays ：

• External disk array cabinet
• Internal disk array card
• software configuration

        External disk array cabinet ： Most commonly used on large servers , Heat exchangeable (Hot Swap) Characteristics of , But the prices of these products are very expensive .
        Internal disk array card ： Cheapness , However, higher installation technology is required , Suitable for technicians . The hardware array can provide online expansion 、 Dynamically change the array level 、 Automatic data recovery 、 Drive roaming 、 Super buffer and other functions . It can provide performance 、 Data protection 、 reliability 、 Availability and manageability solutions . The array card is operated by a dedicated processing unit .
        Using software ： It refers to a common device connected through the disk management function provided by the network operating system itself SCSI Multiple hard disks on the card are configured as logical disks , Make an array . Software array can provide data redundancy , But the performance of the disk subsystem will be reduced , Some of the reductions are quite large , reach 30% about . Therefore, it will drag down the speed of the machine , Not suitable for servers with large data traffic .

3 Cheap redundant disk array

        Through hardware / Software technology , Consolidate multiple smaller disks into one large disk , Not only can data be stored , It can also provide some protection for data ;
        Different RAID Level of functionality 、 The characteristics are also different ;

        ① frequently-used RAID Level introduction ：

1. RAID 0 Strip mode ： The same document is scattered on different disks , Write data in parallel to improve efficiency
2. RAID 1 Mirror mode ： Copy a document into multiple copies , Write to different disks , Quite a few copies of data , Improve data reliability
3. RAID 5 Cost effective model ： amount to RAID 0 and RAID 1 A compromise of , Yes A piece of disk space for redundancy
4. RAID 10： Integrate RAID 0、RAID 1 The advantages of , Parallel access data 、 Improve disk efficiency 、 Mirror write improves reliability

        ②RAID Comparison of level characteristics ：

        RAID 0： The biggest advantage is that it can double the utilization of hard disk ,IO High performance , But there is no redundancy , If there is a fault , There is no remedy , No fault tolerance

        RAID 1： a RAID 0 Item comparison RAID 1 Data security , But disk utilization is lower than the former ,IO Poor performance , Fault tolerance

        RAID 5： This is a RAID 0 and RAID 1 A compromise of , High storage utilization , There is a redundancy check disk , High safety ,IO Strong performance , Fault tolerance

        RAID 5： This is a RAID 0 and RAID 1 A compromise of , High storage utilization , High safety ,IO Higher performance , Fault tolerance