RAID disk array

1.RAID(redundantarray of Inexpensive Disks): Fault-tolerant low-cost disk array,RAID can be through hardware or software technology, Consolidate multiple smaller disks into a larger disk device, giving them better performance.

2.raid-0: Isometric mode, better performance. This mode works better if you use disks of the same model and capacity. This mode will first cut the disk out of the same amount of chunks (for example,4K), and then when a file to write to RAID , the file will be cut according to the size of the block, and then placed in the various disks. Since each disk will have interleaved data, the data will be placed on each disk in equal amounts when your data is written to RAID. Since each disk will have interleaved data, the data will be stored in equal amounts on each disk when your data is written to RAID. :

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It is visible that the data has been cut and placed on different disks sequentially, so the amount of data per disk is reduced! According to this situation, the more the RAID-0 the better , because each disk is responsible for a lower amount of data, which means that the data can be dispersed so that more than one disk to store, of course, it will become better ! apparently the whole the capacity of the RAID is also getting larger.

However, if there is a serious risk in this way, such as if one disk is damaged, then the file data will be missing, and the file is damaged. As each file is stored in this way, all data on it will be lost and unreadable as long as any one of the RAID-0 disks is damaged.

also, if you use a disk with a different capacity, the performance of the RAID-0 will be reduced.

3.raid-1: (image mode, full backup), this mode is also best need the same disk capacity, preferably identical, if the different disk composition RAID-1, then the disk capacity will be the smallest one of the main! This mode primarily "allows the same data to be kept intact on two or more disks":

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written in a large amount of data by the easy-to-know In the case of RAID-1, the write performance may become very poor. Fortunately, if you are using hardware RAID , the disk array will actively replicate a copy without the use of the system's I/O bus, performance is also possible, if the use of floppy array, may not be very good performance.

the biggest advantage of RAID-1 is probably the data backup, but half of the disk capacity is used for backup, so the total capacity is about half the capacity of the disk. Although the write performance of the RAID-1 is poor, the ability to read is also possible because the data has two copies on different disks, and if multiple processes are reading the same data,the RAID will automatically get the best read balance.

4.raid-0+1,raid-1+0:raid-0+1 is 1) First let the two disks constitute RAID-0, and such a set total of two groups;2 The two groups of RAID-0 are then formed into a group of RAID1. This is raid-1+0. The reverse is raid-1+0.

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5.raid-5:RAID-5 requires at least three disks to form this type of disk array. This type of disk array writes somewhat like RAID-0,but each disk is also joined with a single bit of check data, which records other backup data for rescue when the disk is damaged.

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each time a loop is written, a portion of the same check code is recorded, and the recorded same check code is recorded on a different disk each time, so any disk that is damaged can be rebuilt on the original disk by checking the other disk. However, it is important to note that because of the same check code, the capacity of the RAID5 is reduced by one for the total number of disks. When the number of damaged disks is greater than or equal to two, the entire set of RAID5 data is destroyed because the RAID5 preset can only support the damage of one disk.

in Reading and writing performance, read the performance is good, but write the performance generally, this is because to write The RAID5 data also has to be computed by the same bit check code. As a result of this calculation of the action, so the performance of writing with the system hardware relationship is large! In particular, when using a software disk array, the parity check is calculated through the CPU rather than the full-time disk array card, so the performance needs to be evaluated.

because RAID5 can only support one disk damage, so come in there is another development level, that is RAID-6, this RAID-6 uses two disk capacity as parity storage, As a result, the overall disk capacity will be less than two, but the number of disks allowed to error can reach two.

6. Pre-disk function: When the disk array disk is damaged, then a new disk is replaced. After switching to a new disk and starting the disk array successfully, the disk array will proactively rebuild the broken disk data onto the new disk. However, we still have to pull the hard drive, it usually has to shut down in order to do so, the diskis one or more disk spare is not included in the disk array, when the disk is damaged, the disk array will be actively pulled into the disk array, and then rebuilt, You just have to replace the original disk and insert the new disk and mark it as spare disk .

7. Advantages of the disk array:1) data security, reliability,2) better read and write performance, 3) capacity expansion.

This article is from "Tiger Brother's Blog" blog, please be sure to keep this source http://7613577.blog.51cto.com/7603577/1585265

RAID disk array