Simple introduction and difference between RAID and dual-machine hot spare

A. RAID Technology detailed

RAIDis Englishredundant Array of independent Disksthe abbreviation, translated into Chinese means"Redundant array of independent disks", sometimes referred to as a disk array (Disk Array).

Simply put, RAID is a combination of multiple separate hard disks (physical hard disks) in different ways to form a hard disk group (logical hard disk), providing higher storage performance than a single hard drive and providing data backup technology. Different ways of composing a disk array become RAID level (RAID levels). The function of data backup is that when the user data is damaged, the data can be recovered by using the backup information, thus guaranteeing the security of user data. As the user looks, the group of disks is like a hard disk, which the user can partition, format, and so on. In summary, the operation of the disk array is identical to a single hard drive. The difference is that the disk array is much faster to store than a single drive and can provide automatic data backup.

RAID technology Two major features: first, speed, two is security, because of these two advantages, RAID technology was used in the Advanced Server SCSI interface of the hard disk system, with the development of computer technology in recent years, the speed of the PC CPU has entered the GHz era. IDE interface of hard disk is also unwilling to be outdone, successively launched ATA66 and ATA100 hard disk. This makes it possible for RAID technology to be applied to a low-or even personal pc. RAID is typically performed by a RAID controller in a hard disk array tower or a computer.

RAID technology has evolved and now has a basic RAID level ranging from RAID 0 to 67. In addition, there are a number of basic RAID level combinations, such as RAID 0 and RAID 1 combination, RAID (RAID 0 and RAID 5 combination), etc. Different RAID levels represent different storage performance, data security, and storage costs. But the most commonly used are the following types of RAID.

(1) RAID 0
(2) RAID 1
(3) RAID 0+1
(4) RAID 3
(5) RAID 5

The choice of RAID level has three main factors: availability (data redundancy), performance, and cost. If availability is not required, select RAID0 for best performance. If availability and performance are important and cost is not a major factor, select RAID 1 based on the number of drives. If availability, cost, and performance are equally important, choose RAID3, RAID5 based on the average data transfer and the number of hard disks.

Most commonly used for, 1,3,5

RAID Level 1 uses disk Mirror technology, which is to copy the contents of one hard drive to another hard disk, so it has the ability of backup and fault tolerance, so it is inefficient, but high reliability.

RAID Level 3 uses byte-interleaving (Data interleaved storage) technology, the hard disk under the SCSI control card simultaneous action, and the use of parity data stored in a specific hard disk drive, it has a fault tolerance, the efficiency of the drive is installed to lose one of a few, It has a better reliability

RAID Level 5 uses disk Striping (hard disk partitioning) technology, and level 3 differs in that it stores parity data on each hard drive, each hard drive is under the control of the SCSI control card parallel action, fault tolerance, and level 3, The efficiency of its use is also to install a few and then lose one

two. The realization method of dual-machine hot standby

The concept of dual-machine hot preparation includes both generalized and narrow meanings.

Broadly speaking, it is for important services, using two servers, backing up each other, and executing the same service together. When one server fails, a service task can be performed by another server, which automatically ensures that the system can provide continuous service without the need for manual intervention.

Dual-Machine hot standby is an issue where the service is not interrupted when the primary server fails due to an alternate server. However, in the actual application, there may be multiple servers, that is, the server cluster.

Dual-machine hot standby typically requires a shared storage device. In some cases, however, two separate servers can be used.

The realization of dual-machine hot standby, need to pass professional cluster software or dual-computer software.

In the narrow sense, the hot standby of two machines refers to the server hot standby based on Active/standby mode. Server data includes database data written to two or more servers at the same time, or using a shared storage device. Only one server is running at the same time. When one of the servers running fails to start, another backup server will activate the standby machine via software diagnostics (usually through heartbeat diagnosis) to ensure that the application is fully restored to normal use in a short period of time.

Dual-machine heat with two implementation modes, one is based on shared storage devices, the other is not shared storage devices, generally referred to as pure software mode.

Dual-Machine hot standby based on storage sharing is the most standard scheme for dual-machine hot standby.

In this way, two servers are used, using a shared storage device (a disk array enclosure or a storage Area network SAN). The two servers can be used in different ways, such as mutual preparation, master-slave, parallel. In the course of the work, the two servers will be provided with a virtual IP address to the external service, depending on the mode of work, the service request sent to one of the servers to assume. At the same time, the server detects the state of the other server through the heartbeat line, which is often done by establishing a private network. When one server fails, another server makes a decision based on the heartbeat detection and switches to take over the service. For the user, the process is fully automated and completed in a very short period of time, thus not impacting the business. Because of the use of shared storage devices, both servers are actually using the same data, which is managed by a dual-machine or cluster software.

three. The difference between hot standby and RAID on two machines

Some users have a problem when planning a two-machine hot standby or dual-machine backup: I already have raid, and tape backup, and do I have to do a dual machine? Or, if I do a two-machine backup, is it necessary to do a tape backup?

It should be said that raid and data backup are important. However, RAID technology only solves the problem with the hard disk, and the backup only resolves the recovery after a system problem has occurred. And once the server itself problems, whether it is the hardware of the device or the problem of software system, will cause service interruption. Therefore, RAID and data backup technology do not solve the problem of avoiding service interruption. Dual-machine is also very important for systems that require continuous and reliable application services. Just think about it, if your server is broken, how much time you have to restore it to work, and how long your users can tolerate recovery time to understand the importance of a dual machine.

On the other hand, RAID and tape backup are also very much needed. For raid, the reliability of the system can be greatly improved at a very low cost, and its complexity is much lower than that of the dual machine. Because after all, the hard disk is the most mechanical operation, the most vulnerable parts, if the use of RAID, the failure of the system can be easily repaired, but also reduce the number of server downtime to switch.

Data backup is an essential measure. It's a real-time backup, whether it's raid or dual-machine. Any software errors, virus effects, misoperation, etc., will be affected synchronously in multiple copies of the data. Therefore, be sure to make a backup of the data (whichever media you take, it is recommended that you have at least one offline backup) so that you can recover data if it is corrupted or lost

Simple introduction and difference between RAID and dual-machine hot spare