A disk consisting of
two disks properties.
Three RAID:. Redundant array of independent disks
separate redundant array of hard disks,
features:
- By striping the data on the disk, the data is accessed in blocks, the mechanical seek time of the disk is reduced, and the data access speed is improved
- By simultaneously reading several disks in an array, the mechanical seek time of the disks is reduced and the data access speed is improved
- By mirroring or storing parity information, redundant protection of data is achieved
4. RAID data organization form
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-Capacity = number of heads × number of cylinders × number of sectors 512 1MB = 1024KB 1KB = 1024B
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Stripe unit (strip unit): a single or multiple consecutive sectors in the hard disk form a stripe unit
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Stripe: A set of striped units that agree to the same position (or the same number) of multiple hard drives in the hard disk display
5 RAID0
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RAID 0 is the simplest form of forming a disk array. It only needs more than 2 hard disks. The cost is low, which can improve the performance and throughput of the entire disk. RAID 0 does not provide redundancy or error repair capabilities, but it achieves The cost is the lowest.
advantage:
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The biggest advantage is that the capacity of the hard disk can be increased by a factor of 2
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Fast speed
Disadvantages: -
The entire system is very unreliable, and if a failure occurs, no remedy can be performed
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The biggest disadvantage is that if any one hard disk fails, the entire system will be destroyed, and the reliability is only 1 / N of a single hard disk
6. RAID 1
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RAID 1 mainly implements disk mirroring through secondary read and write, so the load of the disk controller is also quite large, especially in an environment where data is frequently written. In order to avoid performance bottlenecks, it is necessary to use multiple disk controllers
advantage:
- Has good disk redundancy
Disadvantages:
- The disk utilization rate is 50%. In terms of four 80GB hard drives, the available disk space is only 160GB.
- In addition, the RAID system with hard disk failure is no longer reliable, and the damaged hard disk should be replaced in time, otherwise the remaining mirror disk will also have problems
- The load of the disk controller is also quite heavy, especially in an environment where frequent data writing is required
RAID 0 + 1
- The combination of RAID0 and RAID1 technology, in addition to the data is distributed on multiple disks, each disk has its physical mirror disk. RAID0 + 1 to establish a stripe set in disk mirroring at least 4 hard drives
- Provides full redundancy, allows one or more disk failures without affecting data availability, and has fast read / write capabilities
RAID 3 (Parallel transmission with parity code)
- You can only check for errors and not correct them. It processes one band at a time when accessing data, which can increase the
speed of reading and writing - RAID 3 can provide a good transfer rate for large amounts of continuous data, but for random data, the parity disk will become the bottleneck of the write operation
RAID 5 (distributed parity independent disk structure)
- Parity codes exist on all disks, where p0 represents the parity value of the 0th band
- The read efficiency of RAID5 is very high, the write efficiency is average, and the block collective access efficiency is good
advantage:
- Parity codes are on different disks, so reliability is improved
Disadvantages:
- In RAID 5, there is a "write loss", that is, each write operation will generate four actual read / write operations, of which two old data and parity information are read, and two new data and parity information are written
