06- Common RAID technology

06-common RAID technology

?? Written by Zak Zhu

Reference

• Honghu Forum
• HCNA-Storage training materials V4.0
• YuTian Zou Sir HCNA-Stor video

RAID basic concept

RAID – Redundant Array of Independent Disks

The emergence of RAID technology The original intention was to combine multiple small-capacity hard drives to obtain greater storage capacity. Currently, the RAID technology we are talking about is more related to data protection. In other words, RAID can be used to prevent data when a physical device fails The loss of data.

The main function of RAID:

• By striping the data on the hard disk, the data can be accessed in blocks
• By simultaneously reading several hard drives in an array, parallel access to data is achieved
• Data redundancy protection is achieved through mirroring or parity information

ul>

RAID data organization form



RAID data protection method



RAID0



• Among all RAID levels, RAID0 (also known as striped RAID) has the highest storage performance. RAID0 uses striping technology Store data in all hard disks in the RAID group
• A RAID0 contains at least 2 member disks. In the RAID composed of two hard disks as shown in the figure above: the first two pieces of data are written to the stripe 0, where the first data block is written on strip 0 of hard disk 1, and the second data block is stored in parallel on strip 0 of hard disk 2; at this time, the next data block is written to hard disk 1 On the next stripe (strip 1), and so on. In this way, I/O load balancing is distributed across all hard disks in the RAID, because the speed on the data transmission bus is much faster than the hard disk read and write speed , So the hard disks in the RAID group can be considered to be reading and writing at the same time
• The hard disks in a RAID0 hard disk group must have the same size and speed. If a RAID0 consists of 4 hard disks, the read and write speed In theory, it can be up to 4 times of a single hard disk, and the capacity is 4 times of a single hard disk. The read and write performance of a RAID0 group is proportional to the number of hard disks.

---

RAID1

RAID1 is mainly used for server hard disk installation system



• RAID1 (also known as mirrored RAID). RAID1 uses 2 identical hard drives and mirroring is set up. When data is written to one hard drive , A copy of the data will be stored on the mirrored hard drive at the same time. When the source hard drive fails, the mirrored hard drive will take over the service from the source hard drive to ensure the continuity of the service. The mirrored drive is used as a backup to provide For high data reliability
• The amount of data stored in a RAID1 group is only the capacity of a single hard disk, and the other hard disk stores a copy of the data.
• The two hard disks of RAID1 must be the same The size of
• The write performance of RAID1 is equal to the write performance of 1 hard drive
• The read performance of RAID1 is equal to the sum of the read performance of 2 hard drives

---

RAID5



< ul>

• RAID5 uses distributed parity, each member hard disk will be used to store user data and parity data
• Assuming that the number of hard disks in a RAID5 is N, of which valid user data The storage capacity is the capacity of N-1 hard disks.
• The capacity and rotation speed of the member disks of RAID5 must be the same
• If 2 hard disks fail in RAID5, the data of the hard disk group will be changed. Lost

RAID5 data writing:

• In RAID5, data is written to the disk group in striped form Each hard disk in the hard disk group stores data blocks and parity information. During continuous writing, the parity data of different strips is not stored separately in a fixed parity disk, but is stored separately according to a certain rule
• When the newly written data is less or the previously stored data has changed, according to the working principle of RAID5, it is still necessary to read all the hard disks in order to recalculate the new parity value. This requires additional Read and write operations, as opposed to writing data to a single hard disk, do not improve the performance of the hard disk. They are called write penalty
• Without considering the write penalty, the full score is written. In this case, the sequential IO write performance of RAID5 is equal to N-1 times the write performance of a single hard disk

Data read of RAID5:

• RAID5 data is stored on hard disks in striped form. All data can be recovered with only N-1 hard disks.
• The read performance of RAID5 depends on the amount of data written and the RAID The number of hard drives in the group

Applicable scenarios for RAID5:

• < strong>Suitable for sequential large IO storage, such as video surveillance storage
• Suitable for SAS hard disks with good hard disk stability

< hr>

RAID6

RAID6 overview:

• RAID with two parity algorithms
• At least N+2 (N>2) hard drives are required to form an array, which is generally used in application scenarios with extremely high data reliability and availability requirements

RAID6 P+ QWorking principle:

How RAID6 DP works:

Applicable scenarios for RAID6:

• Data is very important and needs to be online and usable for as long as possible
• Suitable for sequential large IO storage, such as video surveillance storage
• Suitable for SATA hard drives with poor hard drive stability< /li>

---

hybrid RAID-RAID 10

Suitable for random small IO storage

• For large For most enterprise customers, RAID0 is not a truly operational choice, and RAID1 is limited by the utilization of hard disk capacity. RAID 10 combines RAID1 and RAID0, providing a better solution, especially in random small IO writes In time, because there is no write Penalty, the performance advantage is obvious

• The number of hard disks in RAID 10 is 2N. The hard disk capacity and speed must be the same

• In the above figure, physical hard disks 1 and 2 form a RAID1, and physical hard disks 3 and 4 form another RAID1. These two RAID1 subgroups form RAID0.

• RAID 10 write When data is imported, the data blocks are written in parallel between subgroups, and the data in the subgroups are written in mirroring mode.

Contents

• 06 -Common RAID technology
  • Reference
  • Basic RAID concept
  • RAID data organization form
  • RAID data protection method
  • RAID0
  • RAID1
  • RAID5
  • RAID6
  • Hybrid RAID-RAID 10