RAID array

Introduction to the

Redundant Arrays (RAID) refers to a Redundant array of Independent Disks.

A disk array consists of many independent disks combined into a disk group with a large capacity. The disk array uses the data provided by individual disks to improve the performance of the entire disk system. With this technology, data is sliced into many sections and stored separately on individual hard drives.

The common RAID types are RAID 0,RAID1,RAID 5, RAID6, AND RAID1+0.

Array card

An array card is a board used to implement RAID functions. It usually consists of a series of components such as the 1/0 processor, hard disk controller, hard disk connector, and cache. Different RAID levels are supported. IDE, SCSI, SATA, and SAS ports on RAID cards, such as RAID1+0

RAID level (Level)

RAID 0 (Strip volume)

  • At least two hard disks are required (n≥2)
  • Need to be more than two pieces of hard disk raid reorganization, continuous segmentation for the unit with the bits or bytes data, the file data is divided into several parts, separately recorded all hard disks for storage, so he has a high data transfer rate, but he has no data redundancy (backup), if the disk group with hard disk is damaged, the whole raid will fail;
  • Features: Yes High transmission rate, poor security, cannot be used in scenarios with high security.

RAID 1 (Mirrored Volume)

  • Need more than an even number of hard disks (n=2,4,6…..)

  • Data redundancy is realized through disk data mirroring, which generates mutually backup data on pairs of independent disks.
  • For example, if A1 stores a file, RIAD will save the file to the invisible image A1. When the original hard disk in A1 fails, RIAD will directly extract the file from the hard disk of image A1 and convert image A1 to A1.
  • Features: The disk array has the highest unit cost among disk arrays, but has high data security and availability. When a disk fails, the system automatically switches to the mirror disk to read and write data without regrouping failed data.

RAID 5 (Checkable fault-tolerant volume)

  • At least three hard disks (n≥3)
  • A disk array with a special verification mechanism stores a piece of data in segments to each disk with an associated verification data. A disk group uses a disk as a data verification disk for data recovery.
  • Features: The read and write performance is high, but the check mechanism provides poor write performance and high security. The check data on one disk is damaged and the check data on other disks is restored without affecting other data.

RAID 6 (raiD5-based upgrade)

  • At least four hard disks (n≥4) are required.
  • If RAID 5 has one parity disk, a second independent parity data block is added for RAID 6.
  • Two independent parity systems use different algorithms, even if both disks fail at the same time, data usage will not be affected.
  • Features: Compared with RAID, RAID has higher write loss and lower write performance.

RAID 1+0 (RAID 1+RAID 0)

  • At least four even-numbered hard disks are required (n=4,6,8…)
  • Divide the hard disk group into two groups to form RAID 1, and then create RAID0.
  • Features: Multiple disks simultaneously read and write, high performance, high safety and reliability; A maximum of two hard disks are damaged

RAID hot plate

  • Effect: it is equivalent to a backup in the RAID, such as the original RAID is only allowed to break a disk in the case of the system and data is still normal operation, but the bad two will not work, but after adding hot backup can be broken at the same time two disks are no problem, more insurance.
  • Principle: A hot spare drive is used to make multiple backups for a Raid array. If one drive in the Raid array fails, the hot spare drive replaces the faulty drive and uses the xOR verification algorithm to extract the data on the faulty drive and store it on the hot spare drive. In this case, the Raid array is not damaged. However, replace the faulty drive with another one. The Raid array and hot spare drive are normal again.

conclusion

  • A disk group can have multiple RAID levels.
  • Some RIads can be layered to form a new RAID array, such as RIAD 10(1+0) and RIAD 50(5+0).